Bays are like a lot of old vehicles. Unless you are very capable and can do a lot of the work yourself, to a good standard, buying one to restore is a false economy.
That's fine if you look at it as a hobby and don't mind the costs, spread over time, being higher than the price of a good one in the first place - but in the final calculation, looking at it from a financial viewpoint, the best value for money is to buy a really good one to start with since it will cost less in the end.
Obviously the cost will be relative to which model your looking for but as a rough guide, to get a genuine good camper, your budget would have to be 14k upwards. The very best ones sell for over 20k. You cannot expect to get something good for 8 or even 10k these days IMO.