_I_ think the maximum target price NatAmi may be "good selling" (in Amiga terms, of course) could be something around 450 EUR (anyway less than 500 EUR), if supported by convincing performance/features/enthusiasm.
...even just the plain board (if it's a matter of adding case, drive, keyboard, mouse and so on).
Who knows, maybe it's possible. And time is in their favor - FPGA prices is one of their major cost issues, but FPGA prices are steadily dropping, so maybe they'll get below the 500 mark eventually.
But I think it'll sell in ok numbers (for the Amiga market anyway) - the cost if you want to fully kit out a classic to get even within striking distance of a Natami is pretty steep, and there must be a decent number of crumbling heavily expanded classics out there still aching for replacement.
Pricing out an A1200 mobo only + Indivision AGA mk2 + Subway USB controller + ACA1230/42 gets you to about 470 EUR at Vesalia, and those items aren't even all available, and the 1230/42 will crawl in comparison, and the Natami has SuperAGA, ethernet etc.
You'd be hard pressed to even kit out a classic to similar(ish) specs without resorting to used hardware, and even then you'd likely end up with a big box Amiga with tons of aging and potentially unstable and expensive expansion cards.
If they can beat the fastest expanded classics, I believe there'll be a reasonable number of takers even if they end up at a 700+ EUR price point.
Of course "reasonable" in this case is pretty small. I'm sure the Replay board will be outselling them with a very high factor (not least because it's open and will come with a bunch of cores for other classic computers as well), for example. The Natami is catering for a very specific niche.