If it was in good shape (totally rideable, good cables and tires, clean and greased, no obvious crash damage, no deep scratches or dents, all components fully and smoothly functional) I'd pay $100 for it.

Fit is the entire issue.

Measure the head tube and top tube, or if you know the year you can look up Cannondale catalogs online and find out what the various sizes' dimensinos were that year and measure any unique tube. The use the Competetive Cyclists guide (Bike Fit Calculator | Find Your Bike Size | Competitive Cyclist) to see what might fit.