How to assign a value to a non-cash position in a deal

[Ray Johnson]

We've all heard of the deals where one partner puts in Cash, and the other partner puts in Sweat Equity, Contractor/Site Management, etc..

I'm looking for suggestions on how to assign value to a deal that has an initial non-cash position from one of the partners until escrow closing, then that Non-cash partner will cover 20% of the monthly mortgage on a deal.

Property is in Southern California

Sales price - $650,000 

Appraised at $700,000

New Construction COO 12/01/2020

Owner passed away after 7 months in the new home as to why it's $50k under value at agreed sales price

Partner 1 - 

Sold their home in a not so nice neighborhood and wants to move to a nicer stress free environment. 

Partner 1 proceeds from the previous home sale being used are $200,000.

Partner 1 only earns $49K per year, and has an average credit score, and no reserves. Will not qualify for the loan on the new property by themselves, and cannot afford the monthly payment by themselves. 

Partner 1 will be living in the house as their primary residence.

Partner 1 will be paying 80% of the monthly mortgage cost

Partner 2 - 

Partner 2 has a very high income to qualify for the loan for the property/partnership. Credit score is at 837, has assets for security and underwriting hurdles

Partner 2 is not putting in any cash for the initial down payment.

Partner 2 will cover 20% of the monthly mortgage cost on the deal for the life of the loan. 

Partner 2 found the property for the deal

Partner 1 is planning to live in this home as their primary residence until the end of their life however long that may be. 

The property will be Joint Titled, and both partners are on the loan

I'm trying to figure out how do we figure out what the fair equity positions for the property are going to be.

Does the fact that the property could not have been acquired without Partner 2, account for some sort of equitable value for Partner 2, If so, how do you come up with the value that's doesn't appear to be greedy?

My thoughts are Partner 2 is paying 20% of the monthly mortgage, and should have a 20% stake in the property since they are covering 20% of the monthly mortgage? 

Basically if Partner 2 is asking for a 20% stake in the deal, Partner 2 is saying the Non-cash value of the use of their excellent credit, high income, reserves, assets for underwriting, finding the property, and the risk associated with the joint loan has a Non-cash value worth $40K, which is the equivalent of 20% of the $200K down payment Partner 1 will put into the deal at the close of escrow.  

Are there any other ways to value the Non-cash position, and equity percentage stake in the deal?