In the definition of an on-line group-buying sale (122), a price of a featured item may be specified as a fixed amount, such as $25 per month. As indicated at (124), the sale 122 has an increasing incentive as more buyers (104) join the sale. Buyers (104) make offers as indicated at (126). As more buyers (104) make offers below a maximum threshold, the on-line group-buying sale software (120) increases the incentive as indicated at (128). At the conclusion of the sale (122), the on-line group-buying sale software (120) confirms acceptance of all offers specifying an incentive at or below the final, increased incentive in the sale (122), as indicated at (130). The modified pricing on-line group-buying sale can be applied to a variety of featured items, such as long distance calling plans, rebates for the purchase of an automobile, bank certificates of deposit, or credit instruments, with an increasing number of free long distance minutes, an increasing face value for the rebate, an increasing interest rate for the certificate of deposit, or a lower interest rate for the credit instrument, as more buyers join the sale.