just had 4 vredestein ultrac sessantas delivered from camskills for about £480, as they have a special offer on at the moment for them. thats on 18's.
if you go to rarerims, they sell good wheels, but your looking at a rough price of about £1400 for a wheel and tyre package, and thats with falkens, and they are a relativley low cost tyre, but pretty good quality for everyday driving. i thought about the same thing, but have decided to go for new tyres and a wheel refurb.
you could possibly get a set of rays with tyres off here for around £400 which would last you for 6-12 months depending on mileage, and then upgrade the tyres. don't know if you'll get much on ebay, but you could sell the old alloys.