Vacuforming can be as simple as frame, home oven, and a shop vac. It depends on how much vacuforming that you want to do. A table hooked to a shop vac can make a whole suit of armor. It is only limited by the size frame that will fit into the oven.
Do you want to do lots of pulls? Then you need to build a machine. You can look tthrough reference material and build one on your own (I did), but if you want to skip the trial-and-error part, buy the Protoform plans for $75 and build one for $1000.