Maximum allowable offer Question

[Nigel Ford]

     I have a question. I'm evaluating small multis, and i'm trying to find the maximum allowable offer that still cashflows for me after all projected expenses and the loan payment. What is the most efficient way to do this so that I can have lots of offers to throw out? I can get the maximum P and I payment that works and the present value of the loan from that, but how do I get the purchase price? I appreciate any help on this. 

Thank you, Nigel