Not a lot of info to go on to determine price, but as always -- location matters. These are mine (and Soichiro Honda's, reportedly) favorite bikes. While they don't have as much punch as the 400 they look a lot better, IMHO. But you've got to go check it out in person, and see how it sits. Does it run? When did it last run? History of the bike? Leaks? etc.
Jakec is right, the 350F oem exhaust is the hardest to find; repops go for about $1k. And the black and gold is pretty rare (altough I like the green). 400F exhaust bolts up but you have to use the 400F pegs -- which will set your feet back about 6 inches or so. My 350F with this set up is my profile photo.