^^^ What she said. Ebay, Olympus OM10 with Zuiko 50mm lens, should come in about £20 or thereabouts (lookout for cheap "buy it now" ones, lots of awesome deals). Buy film in Poundland (Ferrania Solaris 200) or Tesco own brand - it's great and really cheap.
As for Polaroids, again - check ebay. Go for a 600 system camera, they're pretty much any one made from about the late 80s onwards I think. 600 film is about the only stuff you can still get. It's hellishly expensive though - works out at about £1 per photo you take (10 shot film cartridge costs about £10-11).
Ones that look like this are the best performing, they come in about a million colours/model names, but are all the same camera. I got one off ebay a year or two back for £4.50, and that included the postage:
These ones are still pretty new (were made in the last few years) and are a lot more portable but not as good: