I've seen some upwards of $40 and more. I am thinking pottery with grooves in it, but don't want to spend $40, unless I have to.
Send Julie Moore, of Dirty Bird Pottery, a message saying what you want. She has a couple of lathering bowls that she will modify with internal changes - spiral groove, horizontal grooves, vertical grooves. She's great.
http://www.dirtybirdpottery.com/shavinggear.html