I recently picked up 34 for $130 or so.
I'm also interested in hearing how people are placing them. I have four directly behind my GB60's right now, but I'll be taking off the inner door panels next weekend to place the rest.
You have me beat, the most I’ve ever used per door is 20. I put 4 directly behind the speaker about 1” apart then the rest in a checkerboard style 3”-4” apart for the rest of the door