Here's what my 10 gallon cost me:
10 gallon tank--> $10.00 (Walmart)
stand--> $25.00 (Walmart)
20lbs live sand--> $20.00 (LFS)
20lbs live rock (figi & tonga) --> $125.00 (LFS)
72watts lighting --> $89.00 (LFS)
10 gallon HOB filter --> $12.00 (Walmart)
2 powerheads, one rotating, one not --> $30.00 (LFS)
tank heater --> $15.00 (Walmart)
Percula clown --> $14.00 (LFS)
Royal Gramma --> $15.00 (LFS)
Various corals from frag auction --> $90.00
Various inverts,....crabs, snails, shrimp, starfish.....--> $50.00
20lbs bag of salt --> $25.00
Grand total of about $520.00. I guess you can skip out on some corals and inverts, but definitely don't skip out on your cleaning crew! Have fun! And like GFK says, "Its a good healthy investment that gives you enjoyment." And it'll keep you out of trouble.