They normally aren't cheap if they have good coloration: I picked up this rock with a huge baseball sized one and two smaller ones on it for $40
My rock of hairy shrooms had three on it, I added a pair of clown fish and the male keeps rubbing on them. Now the large mushroom split into 3, and another is splitting too. It's the first time I watched these ones split, and I want to say the clown fish has triggered the split. Has anyone else had the happen? I am curious since the ones that are splitting are the ones he is rubbing on.