225/45/18's? Good luck... expect your wallet to get raped, hard.
225/40's are very common, but very few cars use 225/45's (only ones I can think of - RX8, MG ZT, M3 fronts) so they are normally very expensive
EDIT - For comparison, in the UK I'm looking for some 225/45/18's atm - I want Falken FK452's, and it's looking like it'll be ~£250-£265, for a pair, fitted
