What kind of lights do you have? Corals like a good stable tank but softies are pretty tolerant. I would say a good starting list would be mushrooms, Xenia, Kenya tree, green star polyps and Zoas/plays. Those can all be cheap to get and all grow like weeds. Oh and start w frags so if any die you're not out a lot of $. Once those start to spread you could move up to some LPS
: hammer, frogspawn, favia, acan, trumpet. Zoas/plays and acans come in all colors but a rule of thumb that I find to be true; the more exotic the color- the harder it is to keep. Good for you green is very common and thus cheaper.