If it were me and had a hitch, I'd go hitch-mount. If no hitch, I'd look into getting one. They install easily enough that one can do it at home. Hitch-mounts offer better fuel mileage, your bikes don't take a beating with rocks and bugs, bikes are easier to access, and there's never a worry of hitting something overhead with your bikes. For what Thule wants for two bike mounts, you can easily get into a hitch-mount (Swagman I paid $100) and hitch (hitchfinder.com). Though, if budget isn't a factor, the Kuat NV is the nicest I've seen. Just throwing some ideas out there.
I'd second this. I had a roof rack for a while and then later installed a hitch rack. (on my toyota corolla) Much easier, for my wife too. Especially for a heavier beach cruiser. I just went to a Uhaul to get the receiver.
You can check craiglist for a hitch mounted bike rack, they are always on there.
Last edited by fourknees; 04-01-12 at 10:14 AM.
Reason: forgot to end the sentence.