Method to "back in" to an offer on a rental?

[Kyle Stratton]

I am relatively new to BP and real estate investing.  I have an opportunity to acquire 4 rentals in one deal.  Each is currently rented, and the combined/total rental is $3,975.  I know what the annual taxes are.  I can estimate insurance, closing costs, etc.  I know what the county tax assessed value is, which I realize is never an "accurate" number for market analysis.  But...

Is there any kind of formula anyone uses to "back in" to a maximum offer price in order to enter into a further negotiation on this deal?

Regards...  Thank you...