The good news is you only need a couple of polyps, 2 will be 6 in a few months with care, one variation below.
Just keep mine that they will spread, average Canadian price $15-25 per polyp. Once completely established Will spread. Some people put them on another rock, then isolate them, so they get no bigger than the rock placed upon.
I have a few, but they are orange, love them, worth the price to me, don't see them often, just the usual colours