Check out the catalogs at http://www.retrocrestliner.com. Guys on the message board there may also contribute to your value question.
As has been said, location is important due to supply and demand effect on pricing. For example, in Minnesota and Wisconsin, boats like this come up for sale often so the prices are lower.
Below is a photo of what to look for on the model/serial number if it is 1957 or newer, which a model 220 would be. This is on my Commander Custom Deluxe model 550 – look under the gunnel on the starboard side up by the front deck. If there are a lot of coats of paint, the stamped numbers may have gotten filled in. Prior to 1957, the Commander model would be an A, followed by the serial number, for example, A-1234. It may be stamped in ink somewhere on the inner transom aluminum, although these stampings have been found elsewhere on some. If it has the Flying Crest logo on the sides instead of the word "Crestliner" it is 1958 or newer. It is not uncommon for registrations to have the wrong year.
By the way, here in Minnesota, I paid $750 about 7 years ago for my top of the line model 550 (only made one year) with a good running 1976 35 Johnson and a very solid, but homemade trailer with like new tires. The boat needs paint, and the seat vinyl needs work, and the transom wood is not correct, being treated pine.
A dual cockpit Commander is a desirable boat!
