Where are you going to sell it? craigslist? ebay? You'll probably realize more profit on ebay than a local sale, unless you are in a metro area. Best determinant of value is by listing on ebay, starting at $0.99 and no reserve, with lots of large, crisp photos, straightforward, well written copy, a fair shipping price, and positive seller feedback.

Zunow is a relatively rare, sought after marque.

My guess is that, depending on condition, the frame alone would sell for at least $400, probably more. The entire bike? Sounds like you've made some upgrades, or is it the original build? Downtube indexed, or modern brifters? Does the drivetrain have lots of life, or is it well worn?

Shot in the dark? $600-$800. Maybe less if well worn. Maybe more if retrofitted with modern Dura-Ace 10 speed.

Set up an email notification search with ebay using the keyword 'zunow'. Watch it for a while. You'll get a better sense of the value.