Counting for inflation $350 is a very good price for one in good shape. Jungle carbine always was a rarer item and a bit of a collector's piece.
At one point people were cutting down mark 4s and selling them as jungle carbines.

About the person who mentioned how they kick. Yes, they sure do!

The question of accuracy is another thing, Am Fear mentions 800 yards. You might be able to hit something at that range, but they were not really made as a sniper rifle.
They were meant to be light enough to carry through the jungles of Burma and south east Asia. The expected range was about 100 yards and they were much more than accurate enough for that.

Jungle carbines make good hunting rifles for bush/forest conditions.
Even though putting a scope on them is a PITA because you need a special scope mount to deal with the shape of the receiver, at least you don't have to change the shape of the bolt handle or anything like that if you really want a scope.
For quick shots at less than a hundred yards a scope isn't really needed.