The only help that I can give you is that your ted williams (Sears brand) model 100 rifle was made by winchester for sears up to 1978.In that year sears quit selling the ted williams brand name firearms.They quit selling all firearms in 1980.
100-400 USD
100-1000 USD and up depending on specifics. proofhouse has sn's
No published sn data.
No published sn data for Ted Williams
Take the first two digits of your serial number, in your case 20 and subtract that from 100. Your gun was made in 1980. Skeeter
That number is the same on almost all model 100, and it is probably 273 which designates Winchester not 278. The serial number on most is under the receiver
No sn data in the public domain.
100-1000 depending on specifics
No sn data in the purblic domain.
MSRP new was $447.00. The serial tells that it was made in 1995 (first 2 #'s minus 100). You could get between 340-400 if it is in PERFECT shape.
50-250 USD or so
50-300 USD or so