How to figure out an offer price?

[April Childers]

Hi, I am a new investor and Realtor, I received a call from some neighborhood prospecting I mailed out. The son manages several investment properties for his mother and he said she would be interested in selling "for the right price". I have looked up the tax records so I know she paid $773k for all of them and have only owned them for about a year. The total rent collected is $11k. I definitely see potential for a deal but I would appreciate any pointers in how to structure it and how to determine a price. I would like to offer a couple of options, one of which would include seller financing. All advice is appreciated. 

R, April