I paid $20 for my 1946 15-91, and it's one of my favorite machines!
1949 was the date that particular serial number was alloted, and I agree with Janice. If the serial number was alloted late in 49, then chances are the machine was made in 1950, and sold in late 50 or in 51.
Does the machine work? Do the attachments come with it? If the cabinet is blonde, what is the condition? Scratches? Dings?
If the price is reasonable, and only YOU can judge that, then get the machine! :)