the days of getting a good straight set of D90's for 300 quid with new rubber and adapters is long gone
you will struggle to get a good set not refurbed for that price (and with porsche size rubber on)
adapters your looking at 150 easy for the set, probable more now (Fk or H&R)
rubber is at least 50 a corner for owt decent and a propper refurb starts at 250 +
then theirs the centre caps

metal ones are expensive, colour crest metal ones even more, and they are just about always tatty and need a refurb which is not easy, believe me i did my badges myself (look in my dubrides thread)
new caps at the dealers are about £40 EACH
oh, and most sets of D90s that come up for sale are 6j front and 8j rears, i had to buy 2 sets and sell the 4 6j's on as a set