Check out
www.worldwidesax.com. He has a number of Martin Tenors and these will give you a good standard of comparison. Dealer prices will be higher than private transactions because a reputable dealer will make sure that the horn is in top playing condition.
For another perspective, Ebay prices for Martin Tenors in this range of serial numbers and going with the description you're provided, generally have
averaged between $1200-1600.00 over the past couple of years, with the majority in the $1200-1300 range.
Or course, with Ebay horns, it's reasonable to assume that one will have to spend additional money to put the horn in top playing condition. I believe that the general rule of thumb is between $300-500.
Given your description that the horn is in "excellent condition" mechanically with the original lacquer, a price somewhere between $1500-1800 would seem reasonable.
But the bottom line is how you like the horn. If it feels right and sounds great, that's it.