Home Value based on area rent and Owner finance

[Wilco Ravestijn]

How do you establish home value based on area rents instead of using a CMA?

The home will be offered as owner finance so no bank qualification needed which is of greater value to a purchaser especially those that can't qualify for a bank loan. Rent in area is $1200. The note Principle and interest will be $1250/month NOT including insurance and taxes. 

I've seen this formula,  annual area average rent * 15. Is this correct?

Thank you in advance.