Hope you can get a picture posted, I'm very curious to see what you've got.
Knowing the manufacturer would be helpful for you to sell, and there are some that are worth more than others, but for most of the badged machines, the condition and what you have that comes with it (Bobbins, attachments, documents, shuttle or bobbin case) are going to be what determines value.
I've picked up treadles from between "free" for ones that were in very poor shape, to $350 for some of the rarer Singer parlor cabinets in mint shape. Now if you have something truly rare or quite old (like pre 1875) that would be different. The only thing you can tell from the patent date is that it wasn't made before that. Wilcox & Gibbs put an early patent date on all their machines, whether they were made a few years after the patent, or 45 years later.