I do not know the current price situation in UK, but in Germany prices for M2 and M3 are going down, roughly 400 GBP on a sound M3 in Cologne. In Hamburg (Leica by Meister) 400 should get you a reasonable one as well. Actually it is harder to find M2 than M3. M4 are going at higher prices like 600, while the later M4-P is closer to 500 GBP. First decision would be 35 or 50 mm shooter? If you are using 50+90 mm lenses the M3 is first choice, if 35 mm is mostly used M2 suits you better. I assume you've read the page at cameraquest before reading this.
Service: Do not worry, CRR Luton does a great job, a complet service is 150 GBP. I picked up an M3 in messy conditions and he did an excellent job getting it back to life and a black paint job as well. Only downside: he is very busy.
So based on a budget of 1000 GBP, you should be able to squeeze in a 50 mm and a 90 mm lens, like a 50 mm Summicron and a 90 mm Summicron Canada, the later can be found in Germany at 250 GBP as a black lens, early chrom ones costing 700 GBP!
I would rather get a Leica body and Voigtländer lenses, a new 35/1.7 or 50/1.5 could be cheaper than a used Leica lens. Leica 90 mm used lenses are rather cheap so I would see no reason to get the 90/3.5.