Pretty much what the others have said. Old and rusty plus the serial number says common. Not a good combination if you want a bunch of money. Markets vary by region too. The last old, rusty, common Singer I bought I paid $5.00 for at an auction. I was the only bidder. I bought another one, older and similar to yours in a treadle table for $25.
The best thing your friend can do is study their local Craig's List and try to get an idea of asking price for similar machines in that condition. Just keep in mind asking price and selling price are two entirely different things. Old sewing machines can be a tough sell.
Rodney