You might search around craigslist to find what they go for in your area.
I'm in San Diego, kegs go anywhere from free but are mostly priced at $40.
We have a guy in town that sells keggles for $95. We also have this guy trying to sell a plasma cut keggle for $220 Converted Keg Homebrew Kettle
If you've got the equipment to cut it, it might be worth the extra $50 or $60 to sell it as a keggle.