I'm perfectly happy with my 800mhz Sam, it much more than 060, Workbench is fast, wb surfing is flawless, I can watch my favorite tv series with it etc. So CPU power is more than OK for me.
Flex would be at least 200€ cheaper without those "industrial" features. Talking about x1000 is different thing, it designed with different way, to offer max CPU power for Amiga and money is not a issue.
ACube might make Amiga only mobo, if there would be enough demand to it. I would say that it is possible to make and sell Flex level mobo about 100€, IF it has only needed features. Just 3x PCI, 2-4 USB, and CPU.
ACube is not exactly BIG player in computer market, so several thousands mobos to sell would be enough to desing and manufacture Amiga only mobo, to get price low as 100€ it would need manufacture in China and at least 10 000 mobos.