Yes, this is Functions territory, unless an app already covers it. Check native automatic discounts first, then public apps built on Functions, and build a custom Function only when neither fits. A buy-X-get-Y rule across specific collections with member tiers is a good candidate, because it combines product rules with customer data.
Cost depends on rule complexity, the admin interface you need and testing. A reasonable planning band for one rule like this is $5,000 to $15,000 to build, plus upkeep for API version changes. Custom apps with Functions need Plus, while public apps built on Functions work on any plan.
Native, app or custom Function
Work down the table and stop at the first row that fits.
| Option | Good for | Limits | Cost |
| Native automatic discount | Standard buy X get Y and percentage or amount off | Limited tier logic | Included in the plan |
| Public app built on Functions | Common tiered, volume and bundle rules | Fixed to what the app offers | Monthly licence, often under about €200 |
| Custom Function | Unique rules, member tiers and collection logic | Needs Plus, a build and upkeep | Build cost plus maintenance |
What Functions can and cannot do for discounts
The limits matter as much as the features.
- One Function can apply product, order and shipping discounts.
- It reads cart lines, buyer identity and metafields on the cart, customer, company and products.
- Discounts can combine with others, based on the stacking rules set on the discount.
- A store can run up to 25 active discount Functions.
- Fetching outside data is limited to custom apps on Plus, and network access must be requested.
- Functions run independently, so they do not know about each other.
How your rule would work
Five steps turn the business rule into a tested discount.
How: keep the tier as a customer metafield or tag that the Function can read.
How: express the collection rules through product data the Function can read.
How: the Function reads cart lines and tier, then discounts or frees the qualifying items.
How: decide how the discount combines with codes and other automatic discounts.
How: mixed carts, tier changes, partial returns and sale items.
What it costs and what it takes to keep it
Budget for the build and for the first year of upkeep.
| Item | Planning range | Notes |
| Build, one discount Function | $5,000 to $15,000 | Planning band, depending on logic, admin interface and testing |
| Published reference | About €24,000 for four Functions | Around €6,000 each in one agency example |
| Upkeep | About €800 a month in that example | Covers API version updates and small logic changes |
| App alternative | Often under about €200 a month | Marketplace licence for standard rules |
- Each Function is tied to an API version, and Shopify typically gives about 12 months to migrate.
- Every deploy creates a version you can roll back.
- Monitor behavior with the Functions logs.
- Name an owner for future rule changes.
App or build
Choose on how standard your rule is, not on how new it sounds.
Rule of thumb: if you need more than one app to imitate a single rule, a custom Function is usually cheaper over a year.
Custom logic in practice
Shopify Functions differentiate payment and delivery methods for B2B and B2C buyers on one store.
Read more: our Easilocks Shopify Plus case study
A custom mini-cart with pre-checkout promo validation and bundles built as variants. Promo code redemption rose from 18 percent to 32 percent, and the custom build saved more than $500 a month in app costs.
Read more: our Rose Inc Shopify case study
Share the exact discount rule, your tiers and your collections, and our Shopify Plus development agency team will tell you whether native settings, an app or a custom Function fits, with a cost range.
Frequently Asked Questions
Custom apps that use Functions or fetch external data need Plus. Public apps built on Functions work on any plan.
Yes. A Function can read customer data and metafields, so a tier can be stored on the customer and used in the rule logic.
Up to 25 active discount Functions per store.
A reasonable planning band for one rule is $5,000 to $15,000 to build, depending on logic, admin interface and testing. One published agency example put four Functions at about €24,000 with about €800 a month for upkeep. Our Shopify Plus development agency team can scope it.
When the rule is standard, an app covers it and the licence costs less than building and maintaining a Function.
