Buddy has an early SN 1895 he's looking to shake. Straight grip, 18" barrel, B00000064. Blue book doesn't give ya too much info. Thoughts on putting a price on it?

Are you sure about the barrel length? The 1895's were re-introduced by Marlin in 1972 or 73 I believe. They came with straight grip, 22" barrels, and a curved hard plastic butt plate. The front sight was in a dovetail directly into the barrel with no ramp. I've had a couple over the years and the B prefix seems right. Working from memory here so I could be wrong. Neither of mine fit into any of the date codes you see online either.

Within a very few years (2-3) they went to the pistol grip with a ramped front sight with 22" barrels. I don't recall an 18" barrel until the Guide gun. It is possible it has been cut. Wouldn't be too hard with the 1/2 mag tube.

I sold my last one 2-3 years ago for $500. I might could have held out for more, but since I only paid $175 for it years ago I did OK I guess.

That is a first or second year of production 1895, the big screws in the studless forend cap and the BO prefix are unique to those two years, I believe they are 71-72 but could be off a year or two. The barrel has been cut and the long mag added, the stock has also been cut for the pad, would have had a curved butt from the factory. It probably also has a different rifling pattern, coarser than Microgroove but not as deep as the later Ballard cut barrels. That rifling pattern is unique to the first two years of production.
The straight stock 1895 was made until 1980, they changed to pistol grip then and didn't make a straight grip again until the Guide gun came out in the 90's. The non crossbolt safety pistol grip guns are the rarest, they were only made from 80-83.

It has been highly modified for sure. How much the modifications impact value, up or down, I have no clue.