The car shade is a good idea. I may have to try that sometime. Handy and functional and not a complete loss when shooting is done. Plus, they would be easy to store.
Along the same lines, we made some out of cardboard and/or plywood covered with aluminum foil. Depending on the mood, we would have foil (crinkled or uncrinkled) taped or glued with the shiny side or the matte side out. Later, we discovered they had some stuff called cinefoil; wow! :o
For the night shots, you could always get some buddies together and try to use their cars headlights. You can always tape some gel in front of them if you like; the lights, not your buddies. A 4x4 with a roll bar topped with lights may be helpful. You will find you will be limited to certain angles, to keep the background from looking like it is lit by headlights, but it may work for you. Just a thought...
For indoor lighting, another idea which is cheap but a little more permanent and costly, is to use coffee cans or the large food service tin cans and mount a lighting socket in them. You can use a variety of lamp types in them but I wouldn't suggest a lamp of more than a couple hundred watts. Each light is fairly limited but you should be able to afford to make a few as they are still cheap (about $15 each). Just make sure you over-insulate (read taped) where the wires enter the can as the tin will cut into the wires in a heartbeat! Of course, you will ultimately be responsible if anything bad should happen. Just some advice and a warning!
Good Luck!