Edd, the Census Bureau is getting pretty granular. They'll have counties/areas down to a 20,000 population online by 2010; they've got it down to (I think) 50,000 now. You can disaggregate the reported data to arrive at some of the numbers.
E.g.:
100,000 population; 2.5 people per household; therefore, there are 40,000 households.
Banks allow, say, 30% of your income to be consumed by a mortgage payment (Roger? How close am I?)
Last sale of subject was $150,000; typical LTV is 90%. Amount financed, $135,000; payment $800± at 6%.
So, to make the cut, a borrower has to make at least $2700/month ($32,000/year).
Now look at the Census figures. How many households in your MSA have incomes above $32,000/year? Knock off the ones who wouldn't consider living in a house that cheap. (Your call)
The number you get will give you a pretty good demand number for SFR's that cost between, say $120-180K. But that sort of thing should be reported as a range anyway. (Pay attention to the error range reported, too.)
After all, they are supply and demand *estimates*, and shouldn't be treated as exact numbers.
