for rental depreciation purposes you use the lower of your total cost less the land cost or Fair Market Value less land FMV when you start renting. assuming each 1/2 is virtually the same depreciation would be based on 1/2 the of the lower of the two values. Property tax bills can be notoriously unreliable as are certain websites that offer valuations and potential sales prices. Asking a realtor in the area would be a good idea. However, I would skip even that if you have reason to believe the property would sell for more than what you paid.
