I just don't know anything about this kind of computer. I can't even find one on eBay so I have absolutely no clue what they are worth in any condition much less its current condition.
As someone who bought a Nova (well, a
clone actually, it's a DCC D-116) in your exact situation, it's... interesting. The thing about the Novas is that they don't get the love nowadays that DEC hardware does.
Bruce Ray of Wild Hare will help you out with docs and maybe software. Parts occasionally come up on Ebay, though they're often mislabeled.
The first thing you're going to want to see is, what's inside the machine. IIRC, the original Nova had 2 boards which made up the CPU (these should be at the bottom), and then however much core, and possibly other I/O. I think your basic Teletype current-loop output was on the CPU boards of the original, so that saves you having to find one of those.
Also, that looks like it's in a rack. What else is there? If there's something like a hard/floppy/cassette/tape drive, that will shoot the potential value waaaay up.
All in all, for JUST the chassis and boards in there, I'd probably pay $75, with no further info. Add to that, for additional goodies.
I'd also recommend testing the PSU outside the machine before powering it up, so it won't burn out the boards if it's overvoltage or something.
You should also be aware of
THIS guy, who wrote an assembler, and is (I think?) working on a C compiler for the Nova line.
EDIT: this is an original Nova. You can tell because there's three rows of blinkenlights.
Also, I'm assuming it doesn't reek of mouse wee or anything obvious. Mouse habitation would obviously tank the value more than any missing component, which (assuming intact boards) can usually all be replaced with standard 74-series and the like.