My goal: create an interest-free loan which is appealing to a potential homebuyer, yet doesn't make too big of a discount on my end.For example: If I sold my $300,000 house with 20% down ($60,000) over 30 years, at 6.7% interest rate: $1548.67 principal and interest per month1548.67 x 12 x 30 = $557,521.20What I would do would offer a lower monthly payment and no usury, but it would effectively be like a prepayment penalty.Arbitrarily, let's say 20% off the monthly payment, or $309.73 less per month: $1238.94 monthly payment.House would be sold at $446,018.40, which is $111,502.8 less than the total paid with a normal mortgage, but $116,018 more than the market price.

Banks and CU have something called "High Cost" rules which means a mortgage under $75K generally is not large enough to include or finance their hard costs plus fee's.Some DSCR lenders offer a $75K minimum after down payment but rates are usually above 9.75% even with good credit and carry a 2-3 year prepayment penalty. 

And we live in CA so our tax rates are high.

I think the general consensus with todays rates and prices is that cash flow is not that amazing in any market. 

Interest rates are really high compared to those of recent years.

Less upfront costs and easier to manage.Most people see the nightly rates of STR and assume the net is higher, but that's not always the case.

In my experience, the best rates and terms for home equity products are from credit unions.

Even at a conservative 8% cap rate the building is worth around $1.625M.

Property is cash flowing and we have long term fixed rate debt.All good.

First, I would comp out what the going rate is for a 5/2 SFR in the same area where the subject property is in.