Assuming you are in full compliance with the contract (a lease is a contract), then the lessor must sell it to you as per the contract. He can neither refuse to sell nor ask for more money than the contract itself provided for. You could bring a lawsuit in county court for a court order forcing him to sell; you have to decide for yourself whether it is worthwhile for you to do this and you are willing go to through with litigation, or if you'd rather either pay his demand amount or else try to settle with him somewhere in the middle.