It is strong money for potentially a lot of trouble but, with the rise in staycations, the campervan market is extremely buoyant at the moment. Its value comes down to its condition and the quality of the conversion. The original Discovery is practically a classic car and most have now been scrapped (often due to rust issues). If it's a rust-free example that's been sympathetically converted into a camper using good materials and the right insulation, £4000 could be a bargain. If it's a rusty heap with a mattress chucked into the back, it probably isn't worth £1000.