What wheels are you currently running ? - the OE standard 16's? - if so then you should have no problem finding a replacement - just put up a wanted thread in the for sale section.
Paying that type of money for rims (&tyres?) won't get you a set any better than the originals - Steelroe has a secondhand set of 18's (I think) in the for sale section - they would be a damn sight better than buying a cheap set of rims - though if I was buying alloys I'd be ideally looking for a set of lightweight 17's - They will cost more but its the most obvious mod you'll make to your car and it won't effect the handling.
Probably an idea to read this post before you go any further -
http://www.fto-ireland.com/forum/phpBB2 ... ght=alloys