Hi Sophie - firstly - in my opinion, anyone asking you for 500 quid to fix a stereo in a 1997 car is trying to rip you off.
You didn't say what's wrong with the stereo (?), but you should have several options:
- look on
for the same radio model, and swap it out. It should be cheap, but be sure to get one with radio security code if it has one. This would hopefully keep any steering stalk controls & remore displays working, if it has any (I don't know the '97 Espace).
- look for almost any aftermarket radio model, new or used, and have someone fit it (Halford fit for free if you buy new). Probably the cheapest option, although you may lose any stalk controls / external display.
There probably other options as well, but all of them should be FAR below 500 quid.
Hope that helps a bit,