Oo, pick me! xD
I just made two coconut caves for each of my bettas and they look awesome. They are real coconuts, and they only cost 2.00 (or 2.30) to get one. You can just break it in half and sand down the edges after rinsing it off and taking off the white part, wich is surprisingly easy if you let it sit out a while. It's very smooth onces you sand it down so it's safe. You might want to soak it first before adding it to the tank and pick off the extra furry looking things on the top of the coconut, and sand that part down a little. That will smooth out the fuzzies.
It does not float, but it is a cool looking cave!