You'll be looking for second hand at that price, and that £500 won't include the labour to fit them. So you are into checking the forums and asking around at reputable tuning places if they know of any sets coming up or for sale. You need to know where the cams came from really as you don't want them from an engine that has gone pop.
The best mix of gains and cost for you would likely be second hand DC5/FD2 cams at that price.
Rough new prices, Drag Cartels are £640 before shipping and import duties, forget anything Toda or Spoon or Japanese for that matter as they are expensive due to the exchange rate, forget Skunk2 as despite them claiming to be DIC they aren't and need springs and tensioner, Buddy Club Spec 1 are £650 and so on it goes.
TDi-North drop in cams are the best results I've personally seen for stage 1s though, but they are £1,500 supplied, fitted and mapped (assuming you already have Kpro/K100).