My press is made mostly of wood (Pine 2x4/6s and MDF). It has 6" discharge hose to pressurize it and will be held together with heavy-duty cloth tubes. This method is quite cost effective, but it's not as sturdy as a press made from steel.
I think for someone looking to press skis on a budget vacuum pressing is probably your top bet. Especially if you don't have a ton of woodworking tools already at your disposal. The forces involved in vacuum pressing are much less than in a pneumatic press, so you don't need to build super strong molds. There's just less bulky, heavy objects to deal with. The most expensive piece is the vacuum pump, which you can salvage out an old refrigerator or buy from ebay. These videos give a great how-to guide for vacuum pressing. http://boardcrafter.com/content/category/4/32/44/
On the other hand vacuum pressing does have some disadvantages. It provides less pressure on the ski. This mainly equates to slightly heavier skis since you're not able to squeeze out as much epoxy. You'll also have to factor in some disposable items for pressing if you go with vacuum. There is special vacuum plastic and sealing tape that you lay down each time you press a ski, and you'll have to buy more for each ski you press.
Pneumatic presses have the advantage that they give you more pressure on the ski and that you don't need to buy any disposable materials for each ski you press. They also tend to end up more expensive than a vacuum press, but if you design everything carefully you can get away with not spending a ton.
Also to note is that if you were to copy what I've done you would likely not be able to finish for under $200. You'd need to factor in $50 maybe in materials that I already had.