What you'll likely find as you search for comparables, is that in stick-shift cars the coupes will bring more money than a comparable convertible. Now M-sport stick convertibles are pretty rare, but the stick isn't always what a convertible buyer is looking for. If you use coupe pricing, you'll likely be high.
Now I'd happily add it to my BMW collection as a week-end car along with my other six convertibles, while I continue to drive my 2013 M-sport 6MT coupe as my daily driver for the rest of my life.
And we can't be more than 110-miles apart!
Good luck
