Personally, anybody that has to ask for everything that they need to run a 2.5 gallon nanoreef really hasn't done enough research to maintain such a tank properly. Small tanks are
-harder- to keep than large ones, espeically in salt water, since salt toxifies every little mistake much more drastically than in freshwater. This can be very hazardous to the health of your inverts.
If you don't have a whole lot of space, but want a nice tank, I would advise you try a planted freshwater tank first. Planted freshwater aquariums can be just as difficult as a salt water reef one. 2.5 gallons is the prefect size for a male betta, or some white clouds or small tetras or small barbs.
Then while your working on your planted aquarium, pruning it nicely and not just growing stuff, give yourself a year to read and digest as much literature as you can on saltwater tanks and reef tanks. Start purchasing piecemeal the things you'll need. I'm on a budget myself, but every two weeks, $10 of my paycheck buys one more part I need for my dream tank in the works. I may not have it until I move to a bigger place, but when I'm all set, I know I'll be prepared.
If you just -have- to have a 2.5 gallon saltwater tank, you're going to be disappointed.
First, nix the idea of polyps and coral inverts. Small tanks limit waterflow, or may have too strong a waterflow for such a small space you'll end up killing them with too much force or two little force. They are planktonic feeders and require a current to carry their food to them. You must have enough time every day to feed every polyp directly, and even that's not the healiest way to do it for them. Overfeeding occures with this method quite freqently, and all that extra food becomes extra excrement, and that will foul the water overnight in 2.5 gallons. Also, like dattack said, most small polyps are going to cost you -more- than a proper set up, and probably be too big for your tank either way. Crowding corals is not healthy, many corals produce an antineighbor-toxin that they fight for growing space with, the victor killing the looser. Too much of the toxin in such a small volume of water will, well, wreak havoc. Water chemistry and quality is also very very important to coral inverst, so you'll want to make sure you have your R/O unit running properly.
Second, you're only looking at -one- very small fish. 2.5 gallons is about enough territory for a damsel, or clown, and, not much else. Most of these fish also grow -large- and will out grow 2.5 gallons within six months to a year. You'll miss out on all the intra as well as inter species interactions by keeping only one fish. Unless you like watching fish kill each other.
Third and most important, you will need to monitor your chemicals -every- day. That's ammonia, pH, nitrites, and nitrates, and do water changes appropriately, I would probably do a half gallon every day if possible. Remember, corals are very water sensitive so you'll probably need to buy or make R/O water. In a fish only tank, most people use dechlorinated tap water with no problems.
To set up a 2.5 gallon saltwater tank, you'll need:
1) A heater to stablize the temps to 76oF
2) A thermometer to make sure temps stay at 76oF
2) 1lbs crushed coral gravel or sand
3) 1 to 1.5lbs live rock
4) R/O unit or access to R/O water
5) 10lbs marine salt
6) Hydrometer to check salinities
7) Ammonia, Nitrite, Nitrate, pH test kits
8) Tap water dechlorinator if you can't use R/O water
9) Power head, a small one if you can find it, or use an
Aquaclear Mini or Whisper Mini filter with no carbons
10) Frozen foods such as brine shrip, Ocean Nutritions Formula Two, and Wardly's Total Marine Color flake
11) Sipon gravel vac for water changes
12) 5 gallon bucket
Keep us posted on how the tank goes.
~~Colesea