Marketvalue is right, when he says it is not a redlining issue. Also, the cost approach proves absolutely nothing on it's own as an indicator of value, I take that back, it shows the highest possible price that a prudent person would pay for something, BUT it does not demonstrate that anyone WOULD pay anything, even $1.00 for the property.
Due to the lack of sale information, marketability, or the possible lack thereof is the issue. What does this mean, it means increased risk to the lender.
Increased risk to the lender means increased cost to you to cover that risk in the form of tighter credit restrictions, as in lower LTV, higher interest rate, shorter term loan, non-fixed rate loan etc, your credit rating needing to be higher etc.
All of these things have absolutely nothing to do with being discriminated against, redling etc. And NO, the financial institution does not have to loan you or anyone else money when the collateral's value cannot be established to a reasonable degree and that is the central crux of the problem. Just becasue Cost Approach Apprasier A says that the property is worth X, does not mean the financial institution must accept that and therefore loan you money anymore than you have to accept a doctors opinion. You may seek a second opinion from what you percieve to be a more competent doctor before proceeding and so may the financial institution.
What it boils down to is that more than likely you are going to have to accept and adjustable rate loan, with a shorter term, or ballon payment at a higher rate than if you were trying to borrow money based on a more typical property who's value could be established witha greater degree of certainty. Just because Mr mortgage hound who screams on TV says rates as low as X, blah blah blah, does not mean this applies to you or your property anymore than 0% interest on Brand X new car applies to the rate and terms you'll pay when buying a 1979 used car.
Find a lender that loans on non-conforming properties and start there. It will save you time and money.