When I posted that first post I didn't have this information handy but this is a cheap alternative to the expensive electric vacuum pumps. And a better alternative to shop vacs. All for $44, a couple of valves and some extra pieces of misc pipe.
www.harborfreight.com
part # 3952-5VGA ($13.99) This is a venturi vacuum pump and REQUIRES that you have an air compressor (90 psi) to function as the power supply to create the vacuum, but it's cheap and does a real good pull for the money
The problem with cheaper vacuum pumps is that they don't pull the volume of air out quick enough, before the plastic cools. To get around this use a tank, vacuum all the air out of the tank in advance and with a simple lever valve turn, it will create an initial and almost immediate vacuum in your chamber, and with the vacuum pump turned on at the same time will continue the pull nice and tight. Here is the a cheap tank, I don't know how good it will hold up to the vacuum but for the hobbiest it should be fine (the worst it could do is collapse
) part # 40057-0VGA ($29.99)
Set it up like this
air compressor - vacuum pump - valve - tank - valve - vacuum chamber
The valves allow for you seal off the pre-vacuumed tank, when it's time to do your pull fire up the air compressor and vacuum pump and as soon as you have the sheet of plastic in place open both valves. POOF