mate's rate; friendship price
A discounted or preferential price offered to a friend, often in informal transactions.
This is a mate's rate, so keep it a secret from others.
I bought a used camera from him at a friendship price.
Almost synonymous; 友人価格 sounds slightly more formal or written, while 友達価格 is more colloquial.
A special price in general, not necessarily limited to friends.
Compound of 友人 (friend) and 価格 (price). A straightforward modern coinage.