I can't see it well, but is that a centennial badge on the machine? Did the gentleman tell you the model? Is there a manual? Attachments? Aside from the model info, these things will also help determine value.
Editted: As best I can see, the serial number starts AK017___
before AK017221, it is a model 15, allotted on Nov. 19, 1950.
If AK017221 or greater, it is a model 66, allotted the same date.