Who has said that they'd be happy to pay €7 for a drink? At the end of the day, the people with the supply will sell at whatever price they feel that they can get away with. It happens in every business in every country in the world. Why should a bar in Perpignan be different?
The only freedom that you have to change that price is the freedom to take your business elsewhere.
Oh, and I bet that I can have a good weekend in Perpignan, have a few drinks and not pay €7 a pop (I know because I've done it).