I picked up this knife at a garage sale at least 20 years ago, I remember getting it for what I thought was a good price (probably less than $50) and it's been sitting in a drawer at my parents house since then. I'm curious what time frame this would have been made and how much it's worth. Completed auctions on eBay seem to be anywhere from $30 to $400+, so I'm not really sure what to ask if I decided to put it up for sale and let somebody else enjoy it. Thanks for any input!

80-125.  it will really depend on the buyer and the overall condition (anything loose?)

looks to be in good shape, has good finish at the top, but has been sharpened (sharpening detracts value, even if it was sharpened 75 years ago... silly)

but in the end, it just depends how bad someone wants it.  the guard marked Camillus is a common knife.  the fiberglass sheath is a plus, but its a bit worn and possibly has a crack on the side near the bottom??

The USN Mark 2 combat knife was heavily produced during WWII.
The early models came in a leather sheath, but those failed to stand up well, so they were changed to a gray fiberglass bayonet type scabbard in the later war period.
Early versions were stamped on the blade, but that weakened it and they could break through the stamps, so later versions were marked on the front of the guard.

During WWII the Mark 2 was heavily issued to ships crews and shore parties, and was the standard knife of UDT Teams.
Some ships ordered all personnel to wear a knife at all times, others only issued them to some personnel when needed.

Enough of the Mark 2's were made during WWII that they were still in Navy inventory through the Vietnam War.
I wouldn't be surprised if a few were still around today.
During Vietnam Navy SEAL and UDT units could get cases of them and they often used them as trading goods to other military units.

These were made by a number of manufacturers, but the most were made by Camillus.

I don't know why it surprises me when someone posts an object, and someone else shows up almost immediately that knows a crapload about the item. Good stuff.

OP, best I can do is tree-fiddy.

Nice