I have the sewing machine below antique dealers say they are only worth sentimental value at the same time they have a very plain basic one selling for $150. so I do not trust antique dealers. They want you to practically donate your antique for a few dollars and turn around and sell them for 150% profit.
Collectors give the best value if it is something they have been searching for.
this site might give you an idea but I have never been able to find a good site on antique sewing machine values and I have really looked because I see this ? a lot.
Selling it on a site like Ebay might work for you too.
How much is my machine worth?