I think what you get depends a lot on how often you're really going to need/use it. This summer we encountered needing one, but since we will only will be using it once a year, at most, we stayed cheap. The Highland universal suits our very limited needs and was at Pep Boys so we were able to avoid shipping charges.
http://www.amazon.com/Highland...uto_1
http://www.amazon.com/Highland...r=8-4
Combined price for the rack and the cargo bag was $80.
It's not the higher quality (or price) of a Yakima or Thule, but if you're only using it once a year it's a cheap alternative. If you're going to use it more often than once or twice a year, buy one of the better ones suggested by others here.