8-unit building, buy it or walk away? What would be a good price?

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I'm looking at an 8-unit building and need help determining what price would make this a good deal. I will be glad to find out and add any information needed to help. Thanks!

Asking Price is 556k        Appraised Value "Sales comparison approach" 598k         Built in 2004

Decent location in the middle of town

All units currently rented "Units leased are 1 year leases" 

Unit A Leased Dec 2018 $775

Unit B Leased Sept 1 2018 $700

Unit C Leased Nov 2018 $900

Unit D Same renter for 3 years, month to month current rent $850, they are upping the rent to $900 in Feb 2019

Unit E Leased Oct 2018 $900

Unit F same renter for 2 years, month to month current rent $850, they are upping the rent to $900 in Feb 2019

Unit G Leased in April 7 2018- March 31, 2019 $700 

Unit H same renter for 3 years, month to month current rent $675, they are upping rent to $725 in Feb 2019

Total current income = $6,350   After rent increase next month income will be $6500

Expenses 

- Tax $817

- Est. Insurance $709

- Garbage $225

- Lawn $150

- Utilities Tenant pays

I have not had the place inspected, but I've seen pictures and figure around 15k in initial repairs. The roof will need to be replaced within 6 years, and assuming a few other things as well. What is the best way to conclude an offer price? How much should I figure in for cap x and repairs is a big one for me. What's a good price per unit to set aside assuming everything's in good condition when you buy it and you can do the repairs yourself? 

Walk away or make it happen? Thanks for any support!