Selling the remaining time on my lease

So I own a small business and have been operating on a 10 year lease for 3 1/2 years. The space next to me is small and the landlord has had a hard time leasing it. I received a call today telling me that there was a "corporate" interest in my location, and they asked me if I was interested in moving or simply exiting my lease. There are 6 1/2 years left on the lease.

My question is...If I were willing to exit my lease for a new business that is going to be leasing my space and the empty space next to me, how should I go about determining the value of my lease? I want to contact the landlord and say "Yes I will leave for $X"

Any help is really appreciated. Thank you in advance.