uniform price; flat rate
A price that is the same for all items or customers, often used in retail or service contexts.
All products in this store are sold at a uniform price.
The flat-rate lunch menu is popular.
定価 is a fixed retail price set by the manufacturer, while 均一価格 means all items share the same price regardless of individual value.
一律 is an adverb/no-adjective meaning 'uniformly' or 'across the board', often used for rules or treatment, not specifically for pricing.
Compound of 均一 (uniform) and 価格 (price).