I built a cheap (lol) vac table to make my Emile visors, and total investment in wood, a shop vac, materials and a bunch of plastic to learn how to use it cost me close to 400 bucks. That was an expensive visor, but now I can make more, and I can make other EVA visors too- but my initial investment to finish 1 helmet is probably close to 500 dollars. Spend some time researching what is around you, sometimes you can find a maker space, tech shop, or fellow builder near you that has already made the investment. Then you can learn from them as well, as vacuforming is a skill set unto itself. I had a hard time with buck construction and knowing how much stretch is right in my petg to form my visor.
Good of luck, I hope that I've helped at least a little bit in your search.