Without more information about the condition of the pistol it is not possible to answer you. BUT I can tell you this. In poor condition it is worth $50 in "NEW IN BOX" condition it is worth $250.
"Model 805 Sportster Single Shot"
Impossible to answer.
serial number T170160 would have been made in 1973.
it was made in 1975
Model number, serial number and features. Then ask that question again here with that information.
T427432 was made in 1982.
If it's T123136 it was made in 1972
you need to state the model number not the serial number to get and estimate of value.
It depends on the model, but it usually is on the barrel somewhere or the breech below where you load the pellet or BB.
It depends on the model, but usually it is right on the barrel or the receiver. If it is really old it may not have a serial number. For a time Benjamin and Sheridan did not serialise their rifles.
If it's not on the outside then very possibly it's under the grip cover
What condition is it in, both mechanically and physically. That determines the value
1980 see the link below. See the link for your date of manufacture