yeah, the $20 vacuuformer is awesome, just make sure that you do not overheat the plastic as you can release cyanide gas into your oven... and your lungs!
lexan is a little bit tricky. First you will need to put it in an oven @ 120 degrees for about 10 hours to get all of the moister out of it. Plexy is not fun to work with either. Modified acrylic would be the best bet for homemade formers.