We have one of these racks from Allen Sports on my wife's car. Pretty decent and easy to use. A big plus is that it folds up and stows away if desired.
The Saris Bones mentioned earlier is probably a better rack, though I have never owned one so cannot make a comparison from experience. I've heard nothing but good about the Saris rack, however. You can find them used for under your $100 budget. I also noticed a Saris Solo rack on the Performance website that sells new for about $50.