Your first step is to find a builbable lot, which is virtually impossible in the counties you mention. There are dozens of spot-lot builders who snap up every piece that is available- usually before they even get put on the market. They beat on doors, and buy houses to tear down to get the properties. Unless you're out there doing the same, you're either never going to find anything, or you're going to pay way more than the builders would for the lot.
A word of caution- if you're not familiar with zoning, wetlands, environmental regs, sewer tap costs, etc., you could possibly get burned for 10's of 1,000's of dollars. There's alot of people out there selling non-conforming lots, and if you don't know your way through the zoning process, you could waste years and $$ and end up with a useless piece of dirt.