Not sure what country you're in, but I get mine through a local signwriters. He gets in styrene or ABS and puts very little markup on - 'cause he's a sci-fi fan. Might be worth calling in and checking out your local sign place. Phil
ABS is really your only other option for a good vacuum forming material
I am also building A vacuum form maching and I have been looking this kind of stuff up so if you need any more help feel free to pm me with questions
Seriously, start with styrene, it's much more forgiving and gives sharper details with lower vacuums and has a larger tolerance of heat, whereas ABS needs a lot more vacuum and goes too close to overheating too easily. Move on to ABS once you've made some stuff with styrene.