Phil
Your best bets at that sort of price will be Mercseller or the Gazette which comes with membership of the UK M-B Club. £17-24,000 should get you a pretty decent car, especially if you hunt around and compromise on colour etc. However, the golden rule is bodywork...
Relatively, repairing most everything else is cheap. I picked my car up from service last week and a decent looking 250 was there. Bloke paid £12,000 and, I was told "when we unloaded it, I said " load it back up again, it's a basket case"". Wings/panels apparently barely welded on etc from previous repairs and so while the buyer paid 12k, he's got some huge bills ahead.