Check thrift stores and military surplus stores in your area.

Check discount stores like KMart, Wallyworld, Target, etc.--the athletic dept. will often have great buys in inexpensive synthetic clothing. Also check out places like Campmor--you can find excellent deals there. Campmor's 20* down sleeping bag, although more of a 30* bag, is as light as you can get for the money. It won't last as long as a higher-quality down bag, but if well cared-for, it will last until you get out in the working world, pay off at least part of your student loans and can afford a high-quality down bag.

Look for used stuff, on ebay and on this and other forums.

Check the outlets (REI, backcountry.com, altrec.com, etc.).

Watch for sales, too. Even the Really Expensive Items at REI may be affordable when they have the 20% off member coupons.

In addition to the Verber site other folks have recommended, where there are links to several inexpensive gear lists, there's a "Mark Henley's Ultracheap" gear list on the Gossamer Gear website. Read them all; they'll give you lots of ideas.

You need a sleeping pad not just for comfort but for insulation from the cold ground. You can go to the expensive stores (like REI) and try out the different varieties; then decide what you want. You can probably get along with a simple closed-cell foam pad for now. For something a little more comfortable, look at Gossamer Gear's Nightlight torso length pad.. Even with shipping, it's cheaper than and probably more durable than the Thermarest Z-Rest.