Typical rust for it's age means different things to different people, and there's a lot of other unknowns such as factory 383 four speed? is engine locked? interior totally shot? and others but with info provided I'd guess $8k ish.
Could be a cast crank 383 but because it is a 4-speed it is probably still a forged crank. I have a 71 383 laying around and it has a cast crank, but it was an automatic car and it was 71 only as 72 went to the 400. Pretty rare car for sure!
Looks to be a Sebring Plus. An N code 4-spd with A/C SSP is pretty rare. 5-10K depending on rust and what not. 71 383 with cast crank was only used in 2-bbl with auto.
I have a question. The Plymouth rocket logo or whatever you would call it that is on the panel between the loop bumper and hood on this car. Plymouth started using this in the early 1960’s. Am I wrong that it seemed to fall out of favor after 1967? Then it appears here. How long did Plymouth use it? When was the last time it was used on a car? Was it continuously used in the late 1960’s? Thanks