can anyone tell me what I should be paying for a lnib m-57 4'' with box and tools

Well, that will depend on the exact vintage it is. If it is an early gun from '64 or '65 and has the correct case with the velour interior, it could/would be worth quite a bit more than one from say 1981.

We simply need more info to give a decent estimate. If it is in a presentation case and not just the box, I will take a shot here though, and say that if it is a '70's or early '80's gun, it should be worth right around $700- $800 as you described it.