How do I come up with comparables if the house is the biggest one in the subdivision?

Where are the units renting compared to the market? 

Nor would changing the configuration of lighting, plumbing, etc - the inspector is going to inspect what's there, not compare them to original plans.Other areas will vary, particularly in areas where government tends to be more heavy-handed.

As David mentioned above, buying in expensive markets can be very profitable compared to cheap markets.

Comparables in the area seem to consist of other manufactured homes, "stick-built" homes, and detached homes.

Cost of living is really low compared to other metro areas so housing is affordable.Yes - she is a little rough around the edges but you take the good with the bad and try to improve the latter.

You will find this is a cheap fix compared to the cost of private or bank lenders.Also, for single family ( 1-4) investor loans, Fannie's limits on investor loan is a little more complex than you explain.  

Get multiple quotes and compare them.

Four comparable homes within a 5-block radius have sold for an average price per square foot (I was a local appraiser here for 6 years) that would indicate a sales price between $87,755 and $89,863.

Hi Ian, don't use single family comparables when valuing a 2 family, they are different animals.Try first to use other 2 families in town with different bedroom/bath counts.