I spent $500 total on two pendant-style MH lights (150 watt each). The 55 gallon tank and wooden cabinet stand were on sale together for $160.
For water movement I spent $35 on a hang-on 330 gph filter. The 300 gph venturi-style skimmer cost $50. I bought two 170 gph powerheads from walmart at $18 each.
I got a free heater from school. The glass canopies ran me $24 total. I also got a free thermometer from school. My college also hooked me up with free food, trace elements and additives.
The test kit I bought tests for ammonia, nitrite, nitrate, ph, calcium all for around $50. This kit does a total of around 30 individual tests per bottle I think.
I bought four bags of aragonite sand from the lfs for around $24 each. The bag of live sand I used to seed was $36 or so.
I only have about 7 pounds of live rock right now, and I'm not quite sure what it cost. It was supposed to be $5.99 a pound, but the people at the store I bought it from always knock anywhere from 15-50% off for me.
I think I got a pretty good price on everything but the hydrometer, which cost $15, but no big deal, lol.
My trick on low prices is to shop around, and haggle with the store owners. Remember that fish stores never have the lowest price acceptable on their items. For instance, I got the store I bought my lights from to knock off $100!!!
Another tip is if you have a walmart around you, buy anything you can from there... it is generally cheaper and their return/replacement policiy is unbeatable. Just don't buy livestock from walmart, they tend to be overpriced in that area, with inferior goods.
If you go to college, go visit the science building and see if they have a marine tank. If they do, try to join the club that sponsors it, or at least ask them if you can help. I had to join the astronomy club to help take care of the tank, but in exchange I get free anemones/corals/etc... anything that can be propagated. Another benefit of this is you get a card saying you take car of a college tank, and most lfs's give enormous discounts for this.
ps- anything I left off was on accident.
edit- although walmart may have more expensive fish, they do have a 90 day guarantee on all their fish, which is incredible.