hard to price retro computers sometimes, especially ones with rather common parts.
In general, a retro computer is only worth what a potetinal buyer (or buyers) is willing to pay.
After listening to other's opinion about your build, I'd say 200$ is a good starting price - from there you can see if it sells or if you get any offers close to that.
THEN AGAIN, considering how good that AT case looks, it alone MIGHT be worth 100$ to some. Personally I'm always on the lookout for good looking AT cases with power supplies and small Hard Disks in good condition. Others might be interested in the Matrox Millenium. Personally if I was in a market for such a system max I'd pay is 50$ for the case, 20$ for the video card, 20$ for mainboard + CPU, 30-40$ for the hard disk drive. Working low-speed period correct (for older builds) CD-ROMs are also getting rare, but there are newer drives without any lettering on the front (sony for example) witch look ok on older builds.
Anyway, good luck with the sale!