Hi, I'm a self-proclaimed 221 featherweight amateur historian who owns several of these machines. I've given talks at local quilt shows on them, and learned much of what I know from a gentleman who meticulously studied them (and their subtle differences) for decades. I'm happy to answer any questions that you may have.
Pricing depends on many factors including age, condition, and scarceness of specific machine. For starters, I'd check out the wiring and motor strength/ability.
Price also depends on whether you're looking to machine as a collectible. Oftentimes, for example, cases and machines aren't original to one another, foot control/motor/manual isn't original, etc.
Enjoy
