I have always bought construction grade polyethylene film wherever I could find it. E.g. Home Depot in the U.S. Then I have taped the bag together or used silicone based window fitting goo to seal it up. Cheap and good enough if you are careful. Buying a professional vacuum outlet to connect the bag to the pump is a good idea, but there are alternatives.
How much pressure? As much as I can get without starving the laminate for epoxy or crushing the materials in the bag.

What do you plan to do and what is your budget <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />