This will be a complex appraisal, with many different scenarios that need to be addressed. Some of the major items to be considered are land value (as if vacant), lease income, lease renewal options, discounted value of the improvements, separate highest and best use determinations of the land, the improvements and as combined, current and projected market value, alternative uses and cost to accommodate changes, tax consequences based on your costs and the current value (if sold), are the current lease terms above, below or on par with what is available in the competing markets, etc. A project like this will probably require a minimum of two to four weeks of rather intense work and research.
I did a quick Google search for the Arizonia Gift Clause (look it up if you want more detail), which basically says governments funds cannot be used to enrich a private individual/entity a greater amount than what a non-government entity would pay. Nothing more than they cannot pay more than "Fair Market Value". My guess if this were to ever go to mediation, they would present their appraisal, you would present yours's and the Mediator/Court would arrive at a value based on either of the appraisals, a combination of the appraisals or some off the wall figure.
Obviously, no one responding on this forum have seen any of the appraisals so we cannot answer specific information. Based on your initial comments at least the most recent appraisal provided to you by the College and the one that is 1.5 years old are junk as they only address the vacant land value and do not consider the remaining 11 years of lease income, the future value of the land and improvements discounted back to the current timeframe, and the probability of their extending the lease for another 11 years at an increased rate, if allowed under the lease agreement, etc.
The big thing to remember is you have a lease for at least the next 11 years, and you don't have to sell. If there is a clause in the lease that allows them option to buy it out the lease, I would think a method of determining a fair value has been spelled out. Also, if you decide you want to sell, I would still get an appraisal as there are investors out there who would be interested in purchasing your interest for the right price. Who knows that right price may be more than what the College is offering. You may even be able to request a restricted report which, if done properly, would provide you with enough basic information to decide what a reasonable value may be. The restricted report can always be updated and converted to a more detailed appraisal report, if the need arises.