Well, there are some tools you can get by with by cheaping out on them, and some you shouldn't. Torque wrenches fit in the latter group. I actually ended up buying 2 different ones (both from Sears, but that's not a recommendation, just information) to do 2 different jobs. A Larger one for things like wheel bolts etc that need over 100lb of torque, and a Smaller one for things like coil overs and spark plugs that need smaller amounts of torque applied and for working in tighter areas.
I would suggest you start with a big one, since you're doing your wheels now anyway, and when money permits, buy a smaller one if needed?
Note - Torque wrenches are not hammers, or pry bars! They should actually be handled carefully and not banged around like most tools. Remember, they are for calibrating things, and should be thought of as a tool that needs to be babied

Ooops - Last Note - The instructions U-238 have above are exactly what I do when rotating tires with 1 more step included. I got this from a couple of different tire places "back in the day" so I'm not sure if it's need anymore or not. After driving the car a couple of times, and the rims/tires/brakes have had a couple of heat up / cool down cycles, torque them one last time. I have found bolts that were a tiny bit looser after the cycle, but not sure if that was due to operator error on the re-install or not
