Comps need to be as close as possible in Time, Distance, and Property Discription, also Sold and Pending Sale are good indicators. Now without any comp?? it is going to be difficult. Best would be seek the assitance of an Appraisor or a Real Estate Agent.
You could also work on the Property sheet, from a title/ escrow company, It gives out the current property value (Cost of Land and cost of developement), as also the sale price and the last date of recording, and the current property tax. You may do some math and try and arrive at a figure, do consider the local appreciation, upgrades if any and property condition. Once again it is not going to be easy without any comps.