Depending on condition, $150-$300.
If your model 400 is a semi auto shotgun, with a squarish back to the receiver (something like the Browning Auto-5) these were made for Western Auto by Savage/Stevens/Springfield, and should cross reference to the Mdl 745. The e-commerce side of gunpartscorp.com has a schematic for the Savage 745/ 745C, see if that looks like yours. They DO have some parts available if needed.
the 745 was made from 1941 to 1949, but other Browning A-5 variants were made until 1999
These shotguns are selling for between 150-300 dollars at this time.
Savage 745 Golden.
The serial number is located just forward of the loading port on the bottom of the receiver.
I have two Savage semi-autos. Although the long recoil action guns are very reliable and wonderful shooters, they have almost no re-sale value in today's market. Mine are both in 90% condition, and I bought them for under $200.00 each. Remington model 11 parts interchange with a lot of the model 720, 745, 755A and 775A parts.
30% off of 745= 30% discount applied to 745= 745 - (30% * 745)= 745 - (0.30 * 745)= 745 - 223.5= 521.5
The factors of 745 are: 1 5 149 745
745 is an integer and not really a fraction. However, you could write is as 745/1.