I only know of the club site as well. If you are not a member though there is a £12 charge per night which makes it expensive if you are staying for any length of time and joining might be a better option then.
There are plenty of other sites though if you are willing to travel a bit towards the coast. It may depend on how close you want to be.
Ray is quite correct re the surcharge. I would say however, that Exeter is quite cheap compared to some club sites, so much of the £12 would balance out as opposed to Hiilhead for instance.
Lots of walking from Exeter Racecourse, it just isnt to Exeter B)
I really dont know of anything half decent in Exeter itself, and the various websites dont throw much up.