Depends. How clean is the machine and the treadle cabinet? Is the bobbin carriage, shuttle, etc. there? Does it have attachments? Did you turn the handwheel to see if everything moves freely? Ask if you can stitch with it...(that'll tell you if the bobbin stuff is all there) What decals are on it, are they intact of are most of them scruffed off?
All said and done? It's probably worth $100 if you think it's worth a $100.