I needed a new pollen filter, so got quotes from various places to see how they varied. This isn't meant to be an exhaustive list of places to check, e.g. I didn't try my local motor factors for a Blueprint part. Here are the prices that I found (all parts are for the OEM Toyota part unless otherwise specified) :
Japarts - £28.12 (not sure if this was a Toyota part, I don't think it was)
CheapToyotaParts - £28.00 delivered
LexusPartsDirect - £19.08 delivered
Lexus/Toyota - £18.02 including LOC Gold discount
Needless to say, I bought it from Lexus/Toyota ! If I had been making a special trip to pick the item up, then LexusPartsDirect would have been the cheapest given the cost of the petrol. But don't forget to check Lexus/Toyota for a price when you want something, sometimes they're more expensive but sometimes they're the cheapest ! :D