Well....I think anybody could agree it is pretty-much a given that it's worth more than you paid for it some 20-years ago. I know all mine are.
I am no LH specialist by a long shot, so until I could "see" what you had, I could not make a guess other than to say 20-year old run-of-the-mill 686's are going for from $450-$550 across the country....depending on where you are.
I am sure there are some folks out here that are craving a NL 686 in that barrel length. I realize it being a LH is suppose to make it an oddity....I just don't know what that oddity is with your gun.
Hang in there...the LH "experts" may be along here sooner-or-later. superpilot may make you an offer, but I think he needs to know your asking price, but you don't know what to ask, because you don't know what it's worth...etc....etc. I can tell you what ANYTHING is going to be worth. In the end, it is going to be worth what somebody will pay for it.