Quantity deals

On the product form, add quantity tiers: from this many units, this much off. Once a product has tiers, the customer gets a quantity field and the unit price updates as they change it. Checkout links can pre-fill the quantity.

It does not combine. If a product is also on sale or has a regional price, the customer gets the deepest single discount, never the sum. 20% off for volume and 20% off in a sale is 20% off, not 36%. A coupon still applies on top at checkout.

Pay-what-you-want products, where the customer already sets the price.