it sounds like a very sound decision, cars are just not that essential. If you have an emergency, you can always call a cab! how important a car is also depends on where you live. it's a lot easier in urban areas.
depending on your car, unfortunately you will NOT get blue book for it. We bought a car (a mitsubishi diamonte) for just under blue book last january (10k) from my stepfather. He believed he was giving us a hot deal. we decided we'd sell it for a car that would be better to haul bikes with a few months later. The best offer we got for our car was $6000. that's 4k lower than blue book.
of course if you have a prius or something like that, you're going to do a lot better.
Good luck.