I'm not sure what very good vintage condition means, but lets assume it's in great shape, no chips, still shiny, really nice decals, good case and some accessories. How much you get for it depends on how long you are willing to wait. I'd start at $450.00. If you are willing to wait for the buyer who falls in love, you might get it. If you are in a hurry and the machine has chips and worn decals, it might bring $150.00.
But, people still find them for $50.00.
No one can give you a good answer. A lot depends on how many are out there for sale and how many buyers are looking when you get ready to sell. There are just too many variables. Where, when and condition will determine the price you get.