Robert, the hotels I usually stay at in Perpignan seem to be fully booked. However there are still places at the Ibis near the centre of town..
Hotel Ibis Perpignan Centre: book your Ibis hotel in PERPIGNAN
I've just booked 2 nights arriving on the 31st of August. That'll give me at least a day and a half in Perpignan itself to see the exhibition.
As well as the exhibitions mentioned on the official web site there's also a fringe exhibition. Quite a few shops and restaurants have small exhibitions of photographs.
All in all it makes me aware of just how poor a photographer I am. There's a lot of talent on display.