Yeah when I first used 100B a couple years ago I had a lot of trouble getting it to expose properly, lots of blown out highlights, but now that I have a lot more experience shooting Polaroid, I've recently fallen in love with the stuff. Beautiful tones when you figure it out.
There was seller close to me that was recently selling the stuff for $10 a pack on ebay, but he must be running low because it's almost $20 a pack now. There is an online seller that has them for $13.99 a pack, you can google it and they will show up. I have about 20 packs, so that should last me a little while. But, it's just like most instant peel-apart film nowadays...increasingly rare and becoming more expensive.