Appraising a 3 unit with no comps nearby

[Amanda Rose]

Good afternoon bigger pockets. This is our first post! 

My question is this....

We are under contract on a 3 unit. It is in a neighborhood of single family and duplexes. There hasnt been a 3 unit sold in our city for years. I cant find anything to comp to. Will the appraiser really value it based on the single family and duplexes? That seems like it will be way undervalued. All of the lenders in the area say they are shocked at how low of a price we got the contract for. The building is in great shape. New roof,new windows, new carpet. The vacant units are move in ready. Gross rents on the unit will be in the $2500 range. Im just looking for some insight into how the pro's in here would value this property. 

Thanks

Adam and amanda