Beth,
Great to see someone planning ahead. (Impulse buyer by nature
- so I have to research & remember the stuff before seeing it at the store - Thank God for a good memory
) Good luck with your research. I vote for sun corals, if you can get one for a reasonable price. With the orange & yellow colours, very beautiful & one of the easier to keep non-photo. spp. It's a good rule of thumb to research before buying, even if it means putting a deposit on something at the LFS. It's our responsibility to know whether or not we can keep something alive & healthy.
Good luck. Pssst, I too like having a cave.