main thing i think is to know your crowd...if you already have at least a 100 following of friends and there friends then look at a headliner round you £500 mark and really push your pr and you should do ok . but if its just a small crew and you want it to grow i surgest you put on smaller partys with just good solid residents that play well and grow your crowd untill you hit that 100 - 150 mark then get headliners round 300 to 500 pound mark and then you could cover things better. trouble is £500 sounds a lot to spend and people think you should be able to book a club filler with that...tbh tho is not the case always... is all about the right pr /word of mouth and following, you could be trowing the £500 away if you dont have all of those.
To be fair tho can get some great djs for around £500 just gotta make sure you back it up with right night.

hope that helps.