If you can bide your time there do come some really good bargains on ebay. You could probably get some 18" genuine Honda wheels with nearly new tyres for that sort of money.
I've seen a few sets of 18"
CTR wheels and tyres with less than 1000 miles go for £500.
But FWH is right, it won't cost much to change them over. Probably about £20 if you are able to leave the car with them for the day.