I have actually found that my nano tanks are relatively easy to keep, as long as I stick to hardier species. I have both a five gallong and a ten gallon. They both have biowheel filters on them, and that is all (although some people don't even use filters on nanos, as the live rock will naturally filter your water). Special lighting is also required to keep the coral, as you obviously know already. A heater as well, although in my experience it's best to keep heaters off during the "day" because the lights will warm up the water. But keep a thermometer in and do what works best for your aquarium.
Protein skimmers are used in larger salt aquariums, but really won't fit well in such a small tank. You are really at your max for equipment, lol, but again, it will be perfectly fine.
As to what you need to purchase... I have found that flourescent lights run around 20$ in that size, but it depends on what is available in your area.
Sand is not necessary. In fact, I like to use regular fish tank gravel, as it's easier to syphon and keep clean, but if you want certain blennys or gobies then you will need sand. Look at spending about 10$ for the sand.
The live rock usually runs aroun 7-8$ per pound, and I have found that 3-4 lbs is usually enough in that small of a tank.
The salt water stores near me sell pre-mixed water. I forget what it's called, sorry, but I believe it's O something? It's special water that has all the nitrates removed, so it helps keep a lot of algae from growing. Before I used it, I used regular tap water with dechlorinator, and I had horrible algae problems. But now, I buy it, and have no algae. Where I live, I can get fresh water for 50 cents a lb, or pre-mixed salt water for 1$ a lb, so it's really cheap and easy. If you go with tap water or other water, then you need just salt. I buy the big buckets because I have a 75 gallon as well, so I spend about 50$ a bucket, but you can buy smaller bags for aroun 15$
As far as the fish, I just have 2 clowns in my 5 gallon, along with some mushrooms, star polyps, and a snail. In my 10 gallon, I have 2 clowns, 2 fire fish, some star polyps, some green polyps, some mushrooms, and suprisingly a nice piece of trumpet corral. Again, I stick to hardier fish like percula clowns, and even most damsels like yellow-tailed damsels or green chromis are great in smaller tanks. Fire fish do well, and cardinals also do well (and are beautiful). Just remember, you can't stock salt water like you do fresh water. I also stick to hardier corals like mushrooms and polyps, so water quality doesn't have to be exactly precise and perfect.
EDIT: Although graham offers good advice, it seems to me like some of the stuff is off, and maybe they are calculating for a bigger tank? The protein skimmer on my 75 gallon was 100$, and is larger then a ten gallon tank! In fact, I have never seen one small enough for such a small tank, although I'm sure they exist. T5s are GREAT lights, if you can find them, but again, I've never really seen smaller ones. We have them on the 75 gallon (Two of them at 200$ a piece), but honestly, on my two smaller tanks, i just have regular flourescent bulbs and my coral is thriving
