http://www.etrailer.com/Hitch-Bike-Racks/Rhode-Gear/RG8015221.html
Good reviews and seems to be a good price. In for 1, though I rarely need to carry 4 bikes.
The cheapest I could find this elsewhere was $89 (Amazon). Loading four bikes looks like a stretch, but the reviews look excellent so its hard to go wrong at this price.