Hey Frankie,
Congrats on finding some off market deals, and getting direct contact with the seller, that puts you in a good position right away.
you didn't specify what type of property it is and what the area is like. But I'm just going to assume it's a C class property in a ok neighborhood.
And before firing any kind of offer over I'd ask for some more information, so that you can get a better understanding of the property and the valuation. You'll need the t-12(the trailing 12 months income and expenses) and the rent roll.
But just to give you a down and dirty quick calculation again without knowing anything more apart from the numbers you gave.
On the 8 unit that's rented out at $750 each-
Calculations made on an annual basis
750x8=6000
6000x12=7200
72000x0.1(10%vaccancy)=7,200
72,000-7,200=64,800
64,800x0.5(50%expenses)=32,400
NOI-$32,400
Market cap for C class is about 6-6.5%
So let's be conservative and use 6%
Value is NOI/cap rate
So 32,400/0.06(6%cap)
=$540,000 valuation
You can apply the same calculations to the 6 units and that should also give you and idea of where the value is.
I hope this helps, feel free to reach to me with any further questions, I'll be glad to help In any way I can!
Cheers
Barri