Quoted:
Not that I'd be able to afford one, but it makes me wonder what it would cost for an entirely-new build Stoner 63 replica?
It would really depend more on how many they plan to produce than anything else. There are no parts kits. These guns more or less don't exist anymore. It's not like building an MG-42 clone or refurbishing an old Chevy. Those are relatively cheap stamped parts for small niche markets but, those niches are large enough to get a high enough volume of parts out the door to give a reasonable price to the finished/unfinished product. With this, your cloning an entire weapon system from scratch. Your the only source of parts. It's a wager. The more you make, the more affordable it'll be to the end user but, the more you make, the more risk you take from the product not selling.
Personally, I think it could be done. I don't know where the company is financially but, the Robinson seems to have sold well enough and it wasn't even really a clone. The base M96 goes for around 2k these days which, were it new, wouldn't be all that unreasonable.