I agree with ReefKeeper. You can find nice frags for $20 to $40 usually. Sure, they are only an inch or two long, but watching them grow and expand in your tank makes you feel like you are doing something right. If you buy entire SPS colonies, those can cost several hundreds of dollars.
It's my opinion that it's too soon for you to start adding SPS corals, but there are several types of LPS corals that are hardy and would do well in a new tank. You can get frags of most LPS corals for around $20 apiece. I would recommend starting with something like frogspawn, hammer, torch, bubble coral, fox coral, or a brain coral. Those would all be good choices for a new tank and won't set you back in the triple digits.