Welcome to Gunco - it's a great place to learn, share ideas, and meet other builders
I'm guessing you'd wind up paying $1500-2K for for someone else's hand-built home-made $500 experiment. There'd be no warranty and you'd have to fabricate your own replacement parts, if/when something breaks. If you can build those parts yourself, you wouldn't want to buy someone else's build.
If you're a CII and thinking about copying/producing them, you might find a seller, but so far, each one has been a custom one-of-a-kind. They're built for the fun and the challenge. However, SS's plans have been out for a couple months so we may soon see some standardization
There's a receiver blank for sale right now on Sturm & AKfiles, for around $62 shipped. Building your own would be the way to go. If you've been building AK's for awhile, give it a whirl! After you've invested $400 in materials, if you're cheap like me, it must work. One way or another, bloody fingers sleepless nights broke parts no social life (other than here, which is a good place to be) - you did say you're serious, right? Go for it