Singer500A -- welcome to the boards. Glad you found us.
Although many of us are fans of these sturdy workhorses, they have very little value in general. Probably less than a professional maintenance. When I was in Seattle going rate seemed to be around $20-40. But I'd check with the shop to see if they had a direct line for the machine as a donation or if they knew of a local charity. The weight and lack of a case are drawbacks.
PS/Edit: nice pictures! Many of us have a hard time navigating the picture attaching stuff.