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.