I am assuming you have already searched the thousands of posts about kegerator mini fridge builds.
Try not to buy the cheapest kit you see. You can save money by looking for a local fire safety store, they usually have co2 tanks, converted extinguisers, for way less than new retail and their fill prices are usually better, too. Get a 10 or 20lb tank, don't bother with a 2.5 or 5 lb. Buy a decent 2 gauge regulator, that has a low enough reading so you can read 12lbs easy enough, and get one that has check valves in the shutoffs.
Not all towers and faucets are created equal. Look around. Forward sealing faucets are nice but you can get by with faucet plugs/caps to keep them from sticking.
Look for corny kegs locally on craigslist, or look here in the classified section, there are a few folks selling cornies at very reasonable prices, I just got 4 from insco2.
Get enough 3/16" ID beverage tube to have 8 or 10' for each tap. You don't want a 5' line.
-Ben