I see 1 acre lots in private communities for $30-50K around here. (I know thats freaking expensive.)
Dude, that's cheap compared to the Puget Sound. Even on the outskirts of a small town that's 30 minutes drive from one of the real cities those 1 acre lots in decent neighborhoods are $80-150k. To get down to $50k for an acre you're waaayyy out in the hnterlands or buying a crap lot that nobody wants (flood plain, bad neighborhood, next to a pig farm, etc). And that's after the bursting of the real estate bubble. Maybe there's some acre lots going for cheaper around here, but not anywhere I've found.
FWIW. we had looked into building. Not counting the land, or well, or septic, or electric hookups, or gas hookups, or clearing if wooded, and if it's pretty level at the building site custom homes START at $84/sf. Put a few upgrades into the deal and it doesn't take much to get it north of $100/sf. So out here, to build what you have now would cost $300-400k depending on the particulars.
Tract homes would be cheaper, but not massively. And no-one is doing tract developments on acre lots out here right now that I know of.
We decided not to build becuase the costs were too high compared to what we could buy, even if only a couple years old. We wanted something similar to what you have except a little larger (2500-3000sf). To get that would have cost us at least $500k if we built it. We can buy something that works just as well for $350-400k.
If my wife weren't dead set on staying in the PNW I'd move out of here in a heartbeat and get somewhere more reasonable.