I have't added it up myself but I imagine that by the time you buy a Blade, buffer tube, buffer tube adapter and a folding hinge, it isn't cheap. And you are still stuck with something that doesn't look factory at all.
Assuming you use an average quality folding mechanism and modify your own plate to bolt the hinge on directly. You're going to spend about $75-100 on the folding mech, $20-30 on the tube, and about $45 on the KAK blade. So about $150-200, unless you use like UTG trash. If you go CZC, drop your drawers, the folding mech alone is $215. It looks like it's built as good as it costs. But... you're going to end up around $275-300 and still have a KAK blade on the back. Obviously there are quite few choices for braces and folding mechanisms out there to choose from. The majority of which range from awful looking to, well, the KAK blade.
I think the gun remaining in pistol configuration might play to your benefit as well. It means the stock could be the original folding mechanism and member because it would skirt the need for 922r compliance. If those can be had without the butt plate and hardware cheaper... (not US made...) fingers crossed say < $100 for you. Even if your adapter is $50 and your tail hook is $120. That puts you square in the sweet spot of $250-270 with the most original, and best looking option available. It should be like printing money so long as you keep them going out the door.
If you can roll that package out sub $250, I really don't see why anyone who is not directly doing an SBR would be interested in anything else. You have the best idea I've seen yet.