On your budget, a little live rock, heater, powerheads, and religious weekly water changes is about all your going to get for your $. Seriously, it is better to save up for the right stuff and go minimal in the beginning than it is to buy cheap equipment. You can do a fish only/feather duster tank successfully with just making sure temperature, flow, and biological filtration are good along with weekly water changes until you can afford good equipment, which will lessen the frequency and amount of water changes as you add good equipment to clean the water. Cheapest filtration method is an Algae Turf Scrubber, but unless you buy a Santa Monica 25 scrubber when they come out then you will have to design and build one for your tank (few $ in PVC, lights, screen, and a pump in a container of some kind).