there is a dedicated web site for browning auto 5 shotguns, google it.
I don't think there is an invector plus model. Invector Plus is the choke system Browning uses on newer shotguns.
It will depend on the specific model and its condition. A quick look at the GunsAmerica.com site shows Browning Sweet 16 shotguns listed for anywhere from $650 to $2500.
If you look in Standard Catalog of Firearms, you may be able to identify it and find the approximate value. (Browning shotguns start on page 356 of the Blue Book and go to page 389.) Try the Blue Book of Gun Values on line, go to the link below
AFAIK, Browning never made a model 810.
1971; value could be between 100-1000 depending on the exact model and specifications.
100-5000 USD
$650-$750 depending on condition. Higher price for unfired condition.
what is the value of a browning sweet 16 no. 51003
Browning did not make a Model 11.
Browning never made a Model 51 shotgun.
1903-1939. Value depends on condition. Your definition of excellent might not mean excellent in terms of collectable Browning shotguns. Broad range; a couple of hundred to a couple of thousand.