@Steven M. This is a complicated situation, but @Roger D Jones gave you some great insight and direction for your specific case. He seems to have a very good idea of the mobile home space. As a 27yr appraiser I'll add just a little more general clarification of the valuation consideration/s you have.
In appraisal, there are generally 3 approaches to value - sales comparison, income, & cost.
sales comparison approach is typically best and most reliable for residential real estate (4 units or less), income approach becomes more reliable for commercial properties (5+ or more residential units), and cost approach is better suited for newer builds, unique, and/or income producing properties. And many situations use a combination of the 3 approaches.
The single family house (sfr) is real estate, since it is (presumably) permanently attached to the land, etc. Assuming the MH's are not permanently attached on foundations, those are considered personal property, not real estate. But, they are income producing personal property because of the real estate and the rights that the real estate owner has.
So, as Roger said, you may be able to find relatively similar comparables (recent similar sales) to the Subject (sfr) and get an idea of that value. Then discounting that value by a certain amount or % probably makes sense, since a potential buyer may discount it due to the presence of the MHP (mobile home park). Local experienced realtors or experienced MHP owner/operators may have a better idea of what those discounts might be.
The MH values may be somewhat of a combination of cost and income. Cost would be the cost to replace those MH's minus depreciation (physical wear and tear). And there may be somewhat of a combination of site improvements included (sewer/septic, water service, etc, to the MH sites).
Then the income approach would be looking at the cap rates, as Roger mentioned. Refer back to Roger's post for the specifics.
You have quite a bit going on with this and some of these following considerations may help:
* How much would the vacant land cost
* How much would the sfr cost to replace minus depreciation
* How much would the land with only the sfr be valued by the market
* How much might a typical buyer discount the sfr + land, for the presence of the MH's.
* What is the value of the "right" to have these income producing MH's on the land.
* What is the typical cap rate (expected returns) on a MHP in the area
* What cap rate/returns are YOU wanting
* Obtain a copy of the past 2-3 years financials from the owner, to get an idea of actual income/expenses.
* Verify the "legal non-conforming" status of the MH's. From what you say is that they are not legal to be there based on today's zoning (non-conforming), but they are legal based on when they were installed (legal). Also double/triple verify the conditions in which they can or cannot be replaced - in case of fire, destruction, etc. In some municipalities, you can't rebuild a non-conforming improvement if more than 50% has been destroyed.
All of this should go into your consideration of how much it is worth to the market and to you. And most importantly is what YOU want out of this deal! Valuation only makes sense with respect to what you are willing and able to do to get this deal. There's no easy answer to this valuation problem, but it sounds like an interesting opportunity.
Oh, and as I think about it, this may be perfect for an owner carry situation. Maybe she wants the income as a monthly check as opposed to a windfall sale with potentially higher tax consequences, etc. From what you say, she doesn't want the hassle any more, so take that knowledge and see if there is a mutually beneficial way to structure this deal.
Good luck!
