I bought a used AC conv kit for about 150~200 ( Ican't remember) bucks off the EE. By itself it didn't work in my upper (it was too long by a few mm's). I ended up taking a grinder/sander to it to shave off a few mm's, and replaced the springs with new ones from lakeside machine. now it functions fine with subsonics, high velocity, anything.
and I bought my BDM's from questar. so that should be a good priciing reference.