I'm not going to have an exact answer for you, but our son did it last Jan and he was 48". I *think* I've seen kids smaller than this, but not sure.
I think the cost was a $7.00, but someone may need to correct me.
BTW, there is another rock climbing wall in USF just past the Mummy. It is in an ally and can be easily overlooked. It doesn't look like a traditional rock wall, but works the same way.