How much should I purchase this note for?

[Justin B.]

I'm new to note purchasing, so any help with this situation would be much appreciated.

I'm wanting to purchase a note from a man who owner-financed a property he sold. The selling price was $165k with $15k down, and the $150k was financed at 7%. The woman who purchased the property from him is way behind on her payments, but he doesn't want to go through the foreclosure process. She still owes about $7k in back pay, but he just wants someone to purchase the note. She still owes $135k on it. The ARV of the home is around $250k.

What would be a good range of offers to accept? What sources can back up and inform both me and the financed-owner? He is an elderly gentleman who thinks he should be able to sell the note at face value. I know that is not the case, but I don't know what to base my offer on, or how to explain to him why my offer is reasonable. 

Thanks in advance for the help!