Someone on eBay UK is selling sets of 52mm UV filter, circular polarizer, and lens cap - for 99p! I always need 52mm skylights/UV and caps for the lenses I sell so I just bought a few which arrived today, and they appear to be exactly as described. Probably not up to the highest quality standards, but I'll be honest, I can't tell the difference at all, and they'll certainly keep the dust out well enough. Annoyingly they don't have any other size at anything like this price.
Probably not worth it if you're outside the UK.