uniform fee; flat fee
A single fixed price applied to all customers or items, regardless of usage or distance. Common in pricing for services like taxis, buffets, or shipping.
This taxi company charges a flat fee anywhere in the city.
The all-you-can-eat plan with a uniform price is popular.
定額 refers to a fixed amount of money, often for a subscription or allowance, while 均一料金 emphasizes that the same price applies to everyone or every case.
一律 means 'uniform' or 'across the board' and can modify nouns like 一律料金, but 均一料金 is a set compound specifically for a flat fee.
Compound of 均一 (uniform, equal) and 料金 (fee, charge).