Vacant land is a very specialized area. Is this a finished lot? Or is it a large parcel. If its a large parcel, not part of a PUD, BEFORE making an offer, hire a MAI Appraiser from one of the larger firms in Orlando. Clayton Roper is a place to start.
If its a PUD, call a local lender who specializes in Contruction Perm Mortgages or Lot Loans. Try Wachovia or MI bank. Someone there should be able to point you in the right direction for evaluation.
After you have your price arranged, be sure to do an environmental and a soils test (again if its a non PUD)
There are firms specializing in this : Try McIntosh and Assoc. There is much more to purchasing land than the price.