I only have a maroon clown and a scooter blenny(not recommended) in my 15 gallon. I would recommend getting a small fish or two and a shrimp. Do research on the fish before getting them, it may look small now but its going to raise h*ll if you get the wrong type of fish.
Corals are harder to keep but if you keep your levels maintained there should be no problems. I recommend starting out with some mushrooms or polyps. But it is absolutely nessary you get a good lighting system for your tank. $120-150, should be the decent price for a good lighting system. Either Power Compacts or VHO (very high output), i recommend VHO's they look better in my opinion then power compacts. Mushrooms can be kept in lower lights depending on wattage of the bulb, always check wattage.
I would get a red sea prizm skimmer if your budget is kinda low, fairly good protein skimmer. I would invest in one definitely, once you see what it removes from your tank you will agree. If you are willing to spend a little more then go with CPR a bakpak skimmer.
Filtration, i would get about 15-20 lbs of live rock, and a bag of live sand(20-25lbs usually depending on brand), skip crushed coral. I use the smallest penguin filter because my tank is limited in space because its acrylic.
If price is really limited and you want something simple, i would get a protein skimmer, sand, atleast 10 lbs of live rock, NO lighting, i would get one with two bulbs atleast and a small penguin filter.
good luck