The Porterfield Fast Road/Track R4S (second link) is a good compromise between the cheap and nasty EBC pads(Top link) and the Porterfield full race pad(carbon Kevlars) .
I used these Carbon kevlar R4 pads on the race car for a few seasons and they were very good but exspensive and dusty. Depends how long they need to last mate. For track use I wouldn't use anything cheap, false economy.