Check out Wayne Homes.
$100/sq ft should get you a nice house.
When dad built his last custom house in 2002, he built it for $70/sq ft with corian, 6 panel doors, etc. With the way the economy is, you should be able to get something real nice for $90/sq ft.
Although the cost of building hasn't gone down, the # of housing starts has slowed very dramatically due to the # of existing homes on the market.
Also, you have to budget running electric, water, phone, gas, sewer, cable, and driveway to your place, about $10-$25k depending on how deep you are.