Hello, and thanks for taking the time to read and hopefully answer my questions. 

As per the title, the building I inherited is a ~35000 square foot retail/warehouse building with railroad access on a major highway in northeast Pennsylvania. There is currently a tenant there on a 50 year ground lease that is up next year. The catch is, they have the option to renew for another 50 years at the current lease terms, which barely covers the property taxes on the land. 

My attorney has already contacted them letting them know we are not interested in extending the lease at those terms. It is clear in the lease that all they have to do is notify me in writing that they are going to extend. My attorney, however, tells me that if we are going to have to go to litigation over it, that we would absolutely come out on top. Especially because at the end of the first term the building and infrastructure becomes property of the landlord. This is something I would like to avoid if possible due to the up front cost of going to litigation. So, I have been tasked with coming up with a "fair" number per square foot to give them on a newly drafted lease.

Would it be worth the cost of a Crexi or Costar subscription to pull up comparable properties for lease? Is there a better way of coming up with a reasonable number? 

The tenant is a privately owned company. I have looked through their top public competitors' SEC filings and 10-K forms. On average they are paying $8 - $20 per sqft for their leased properties. That is all over the US though, it is near impossible to find what they are paying regionally. I have been told that the rail connection would be a "multiplier" to the cost per sqft. 

I do not expect to get "market rate" out of them, but I need to come up with something that is fair to me as the landlord. I could really use some advice on this, as I've kind of hit a brick wall on my own. 

What would some of you do in this situation? Does litigation sound like a good idea if necessary? Should I try to find a way to kick them out and find a new tenant at market rate? Am I just screwed for the next 50 years? I'd really appreciate any input on this. Thanks again for reading.