There are not too many lenders in the market lending on land. And more than likely, they will require much more than 20% downpayment. My best bet is look online, for the very few lenders that still takek risk on vacant land.
Interest Rates are also a reflection of the risk that an entity is willing to take. So, for anyone serious to give you relevant information, would have to take a complete application, to see the four factors of analysis: Credit, Income/Employment, Assets and Collateral. With this information, they should be able to determine, LTV, DTI, and other risk indicatives.