Old sewing machines are a dime a dozen. There is some small demand for them from specialized collectors. Almost every household used to include one or two sewing machines, and almost nobody sews anymore,( generalist comparative statement, sewing folks out there forgive me, it is comparative to the old days when everybody's mom, auntie and grandma sewed) there are many more sewing machines available than you might think! If it is in excellent working condition and you have the case/stand,attachments, bobbins, needles, etc, you could maybe get up to $100 for it: but it is a very specialized market and you would have to find just the right buyer, which may take a loooong time. If you want to sell it on ebay or craigslist a fair price would be $35 or so.

From the photo, I believe you have a belt driven model with an electric drive conversion kit. The belt sheave is still on the head wheel. The electric motor drives the head wheel via a friction wheel.