As someone who hates 10K engines that make 400 HP and 50K restorations on 383 B bodies - It sounds steep, and my initial thought is BS rip off.

But when you're having the machine shop disassemble your engine I'm assuming they're doing EVERYTHING. That's going to add up quick for parts and labor. I would say $4,000 to build the short block with the stroker kit for parts and machine work, then add assembly labor. Since you're $500 in already, yeah, labor and dyno time will probably add up to 8K. You're probably going to be $5,500 into the short block, plus heads and valve train, plus dyno time.