It depends on where you are located, the condition of both the machine (and what machine model) and the cabinet for the value. You could check around locally for what is available and the conditions they are in for ideas. Do realize that asking price and actually selling price is two different things.
While sentimental value does not equal dollars and cents, there is little I wouldn't give to have my grandma's treadle.
Enjoy your prize whatever you decide to give for it. Lucky you!