There are external power supplies available that connect directly to a disk. I would be more skeptical regarding I/O-performance. As far as I can see, there are only two SATA-ports available.
It has 4x2ghz Intel Celeron J1900, 4 SATA2 and 2 SATA3 ports and 19V DC input, so no more need for a bulky ATX power supply (though for a NAS you need to find a way to power those hard disks).
Judging from the prices that similarly specced boards are fetching (between 50-70€), this one should be below 100€ as well.
Here is a slide from the Asrock CeBit presentation with the specs: http://4.bp.blogspot.com/-1wOiaMWiiXw/Ux7HGzZAl6I/AAAAAAAAHQ...