Keys are items in Rocket League that can be bought from a player's specific platform's marketplace and used to unlock crates. They can also be traded with other players and are commonly used as "trading money".
On September 23, 2016, Psyonix announced that international key prices for Steam users would be brought inline with USD key prices:
This alignment is necessary because Keys are part of Rocket League's active economy. Some price adjustments are more dramatic than others, but are necessary to reflect the appropriate and approximate value of the keys regardless of your country of purchase.
Prices for PlayStation 4 and Xbox One users would also be updated at a later date.