This has already been said, but all of your questions can be answered by reading the forums on skibuilders. $200 for a press and $150 for skis is probably an unrealistic figure. It can be done, but your press probably won't be constructed well and may end up failing which would be a waste of $200. And you could probably do a ski with wood sidewalls, which isn't necessarily a bad thing, for a little over $150. Also, depending on what you have in your garage, necessary tools including a router, jigsaw, beltsander, compressor, a ton of clamps will cost you at least $500. Not necessary but extremely helpful tools including a planar and tablesaw will cost at least another $400. Not trying to rain on your parade, just stating the facts that $350 will not get you very far in the world of ski building.
Now to answer your question. The most inexpensive dependable method for pressing a ski would probably be a vacuum press. As long as you are not at super high elevation this method should work fine especially for your first press. The pneumatic press is a little better but also more costly. It is possible to luck out and get press materials for free which would help you out a lot, so search for some free metal around your town. There are many threads on this topic on skibuilders so just spend a few hours there and you should be on your way. Hope this was of some help. Best of luck.