Most Shopify back-in-stock apps do the same core job: capture shoppers on a sold-out product, then email them when it returns. Where they differ sharply is how they bill you, and that choice can cost you more the better your store does. There are two common models.
Model 1: pay per notification (or by volume tier)
In a usage-based model, you pay for what the app sends: a price per notification, a monthly allotment of email "credits," or a subscriber/notification tier you graduate through as you grow. It looks cheap at the entry level, which is exactly why it's common.
The problem is structural. Your bill scales with your success. The restock that matters most, a popular product coming back with a big waitlist behind it, is also the one that generates the most billable notifications. So the moment you're recovering the most sales, the app charges you the most to do it. A viral drop that leaves a few thousand people waiting is a great problem to have, right up until it's a line item.
Usage-based pricing also makes your costs hard to predict. You can't know in advance how big a waitlist will get, so you can't know what a restock will cost until after it's sent. That is an awkward way to budget for something whose entire purpose is to be triggered by events outside your control.
Model 2: flat pricing
In a flat model, you pay one predictable price and every notification is included. The size of a waitlist changes nothing about the bill.
That's how Restocked works: $14.99/month, flat, with the first month free. Every product, every variant, every notification is included, with no per-notification charge, no volume tiers, and no usage caps. A restock that alerts 20 people and a restock that alerts 20,000 cost exactly the same.
The trade-off is honesty: a flat plan isn't the absolute cheapest option for a store that sends almost nothing. If you get one restock a quarter with a handful of people waiting, a free tier or a tiny usage plan will beat it. Flat pricing wins as soon as demand is real, and especially when you don't want your alerting bill fighting against your best months.
What the market actually charges
Abstract models are easy to argue about, so here are real numbers. These are the published Shopify App Store prices for four established back-in-stock apps (STOQ by Artos Software, Amp by HEL SG, Swym, and SC by Shop Circle), checked on 4 August 2026. App pricing changes, so treat this as a snapshot and check the listing before you decide anything.
| App | Rating | Free | Paid tiers |
|---|---|---|---|
| STOQ | 5.0 (3,440) | 30 emails/mo | $10 → 1,000/mo · $29 → 2,000/mo · $69 unlimited |
| Amp | 4.9 (823) | 10 notifs/mo | $19 → 500/mo · $49 → 2,000/mo · $99 unlimited |
| Swym | 4.7 (419) | none | $19.99 → 1,000/mo · $59.99 → 10,000/mo · $99.99 → 25,000/mo |
| SC | 4.5 (158) | 50 alerts | $10 unlimited email · $20 (+200 SMS) · $45 (+500 SMS) |
| Restocked | launching | first month free | $14.99 unlimited, at every volume |
Three of the four price by volume. Look down the columns and the shape of the usage model is obvious: the price of sending an alert isn't fixed, it's a function of how many you send.
Working the math at three store sizes
Take the same store at three stages and run it through those plans.
A small store, 200 alerts a month. Almost everything is cheap here. STOQ's $10 tier covers you. Amp's $19 tier covers you. Swym starts at $19.99. SC's $10 email plan covers you. Restocked is $14.99. At this size the flat plan is mid-pack and the honest answer is that the difference is a rounding error against a single recovered sale.
A growing store, 2,000 alerts a month. This is where the models separate. STOQ is $29. Amp is $49. Swym has moved to its $59.99 tier. Restocked is still $14.99. You are now paying two to four times as much on a usage plan for the same job, and nothing about your store changed except that more people wanted things you'd sold out of.
A store with a real drop, 20,000 alerts in a month. Amp requires its $99 unlimited plan. STOQ requires $69. Swym's published tiers top out at 25,000 alerts for $99.99. Restocked is $14.99. The month you most need the alerts to go out is the month the usage plans cost the most.
The pattern is consistent: usage pricing is cheapest when the feature isn't doing much, and most expensive exactly when it is.
Where flat pricing loses, honestly
Two cases, and it's worth naming them rather than pretending they don't exist.
You barely send anything. If a restock is a rare event for you and a handful of people are waiting, several apps have free tiers that will genuinely cost you nothing. STOQ includes 30 emails a month free. Amp includes 10. SC includes 50 alerts. If that covers your actual volume, it covers it, and no flat plan beats free.
You only want email, at the lowest possible price. SC Back in Stock's email-only plan is $10/month for unlimited emails, which is less than Restocked's $14.99. If unlimited email at the lowest sticker price is the only thing you're optimising for, that is the cheaper option and you should know it.
What flat pricing buys instead is the thing usage pricing can't: a bill you can predict before the restock rather than after it, and no incentive to think twice about a big send.
The variables that aren't in the headline price
Comparing sticker prices alone will mislead you, because apps don't count the same things.
What counts as one "notification." Some plans count each email. Some count each alert request (a shopper signing up), which is a different number entirely, and usually larger. A plan advertising "1,000 alert requests" is not the same as one advertising "1,000 emails sent."
Whether SMS shares the quota. Several apps bundle email and SMS into one allowance, or charge SMS separately on top. Amp lists SMS at $0.015 each. SC lists SMS add-ons at $0.10 and $0.09 each depending on plan. If you never send SMS this doesn't matter, and if you do it can dominate the bill.
Whether the quota resets or rolls over. A monthly allowance that resets means an unusually big month can push you into an upgrade for one month, then leave you on the higher plan unless you actively downgrade.
What happens when you exceed it. This is the one to check hardest. Do alerts queue? Stop? Auto-upgrade you? An app that silently stops sending when you hit a cap is failing at the exact moment it's most valuable.
How to tell which one you're looking at
Pricing pages don't always say "usage-based" out loud. On any back-in-stock app, scan the plan for these words:
- "per notification", "email credits", or a send allowance: usage-based.
- subscriber or notification tiers (for example plan jumps at 1k / 5k / 20k): volume-based, which behaves the same way.
- "unlimited" or "all notifications included" with a single price: flat.
Then ask the question that actually matters: what happens to my bill on my biggest restock of the year? If the answer is "it goes up," you're on a usage model.
Where Restocked lands
One price, everything included, first month free, so the cost of recovering a sold-out sale is the same whether the waitlist is small or huge. Restocked is not the cheapest app on this page at low volume, and it doesn't try to be. It's built so that the more the feature works, the less you pay per recovered sale, rather than the other way round.
That's the whole point: the app should make more restocks feel free to send, not tax the ones that pay off most.
Restocked is launching soon on the Shopify App Store.