The Yamaha MD-8 sold for about $1150, new.
I also have the Yamaha MD-8, and I think it's a fine machine, with great sound and high capability. Through a use of DIRECT, or 4-Buss & Direct-mode recording, you can get a genuine 8-simul recording capability,... which is a significant advance over the likes of the Tascam 488mkII.
$400 for a like-new MD-8 is quite fair,& a good price.
About 6 months ago, I got a v-good condition MD-8, (package deal) that included 14 MD-Data discs and TWO half-rack efx units, which brought my NET cost of the MD-8 down to about $350, by my own calculations, and I thought I made a VERY good deal. I've never regretted it, & I shopped MD-8's for a LONG TIME before purchasing.
The MD-8 often sells for $450 or more, on a regular basis. It's a unit that's worth getting. I'd recommend the MD-8 as a standout technical achievement, although dated, which is still alone in it's class.
Good luck!