Rover owners: Rusty arches

Went to get a quote from a local bodyshop about getting my rusty arches done, and they came back at £500 a side. At first I was a little shocked but from reading up that might not be as extortionate as I first thought, however I'm a novice when it comes to bodywork pricing as the only thing I've ever had done was a scrape on my ZS bumper which the dozy woman who drove into me paid for (£80).

For now I've given the rust a good spray with ACF-50 which is meant to protect it and stop it from spreading, it certainly hasn't spread further since buying my Ti a few months back so hopefully it's doing its job but the rust will need addressing before winter.

Could anyone tell me whether £500 per arch is a reasonable price for this kind of work, or alternatively recommend somewhere to get it done? I'm based in Derby and work in Nottingham but don't mind travelling for a reputable place.

Click the pictures for bigger versions, also it doesn't look as bad as this in person but it's hard to take a photo that represents it properly. The first picture is one sid, the second and third are the other side as it's not all over the arch on that side.