Unless you are in a major hurry, take the time to check out both ebay and craigslist....
I have purchased all the pieces for my yakima rack through one or the other..
My wife and I have mountain bikes, but different styles of frames. One of us uses the king cobra, the other an older style lockjaw... picked the lockjaw up really cheaply, spent some cash on newer hardware, and looks great. Pre-owned bars, and towers... again worth the time looking and bidding...
I agree.. if I had to do it again, I would go for the hitch mount... does save time and having to lift the bikes to the roof. And having to watch for low-overhead clearance, but that is another story...
But for camping we have a folding valley carrier for the hitch, with a box and cooler... so the roof was the best option... bought a good three-step ladder to use... which also comes in handy when washing/waxing...