I don't know a good price, but certainly less than $100 for a good condition machine in a good condition cabinet.
I recently got a Singer 128, which is a 3/4 machine. It has the centennial badge on it, but the serial number was allotted in Dec 1949. I am thinking they started putting the badge on machines made in 1950 but sent to dealers starting end of 1950 or in 1951. There is always a lag between manufacture and delivery to the dealer.