Hey Zacman, welcome to the forum! I too was a broke highschool kid skiing until this year when i became a broke college student skiing.
I would definatly advise against sharpening and forgetting them. You wont notice the difference (because you will gradually lose edge hold as your edges gradually become more dull) until you have them sharpened again when you'll wonder how you skiied them before.
Generally every ten days on snow is a good time to get them resharpened, though opinions vary with the type of skiing you do, and the condition of the snow, and your weight, etc,... every ten days is pretty good.
Another good idea is to keep a gummy stone or a small pocket knife sharpening stone in your pocket and at lunch, check the edges for burrs. You can do that by running the tip of your thumb nail along the edge from tip to tail and if it catches, there is a burr. These can develop mostly from skiing over nasty stuff in the snow and can be quickly dispatched with a few light passes with the gummy stone over the area with the burr.
As for the sharpening, there are a vast myriad of expensive and exotic ski files made from strong and abrasion-resistent metals, but all you REALLY need is an 8 inch mill bastard file from the hardware store. It'll run you 5 bux. I also suggest a peice of 2X4 cut that is 4 inches long so you have a square piece of wood. This will act as a guide to keep your file at precisely 90 degrees, though you can spend $15+ if you want to buy an edge bevel guide to experiment with different angles; but for simplicity, nothing beats 90 degrees. [img]smile.gif[/img]
*the ='s are the file, the X's are the ski amd the -'s are the 2X4.
This is a pretty crappy illustration, but i hope it shows how you are supposed to hold the file against the side of the 2X4, with the face of the 2X4 running along the bottom to keep the file at 90 degrees to the base of the ski. Using light, even strokes, you move the file down the ski (from tip to tail) using the guide (in our case a 2X4) to keep it all even and consistent. Unless your skis are badly dulled, you wont need much pressure to sharpen them. after they are sharpened, inspect for burrs, and you are good to go! Remeber though, only sharpened the edge that will touch the snow, dont sharpened it where the ski comes up in the front ( and back also if you have twin-tips).
Also, keep the file away from moisture because the micro-filings of steel ski edge oxidize at an accelerated rate and if the file is exposed to moisture after you used it, very quickly the filings in its grooves will rust and htere is nothing worse than a rusty file. You might as well throw it away, it will contaminate the clean steel in your edges (metalurgy experience talking here)
Hope I didn't overload you with information, I am just trying to pass on the lessons I learned while sharpening my first pair of skis (which I nearly ruined until I got it right