The point about lumber is accurate. We are getting a fence built for our house, and our contractor says the lumber has gone from $12 a board to $28 a board over the last few months. He's had to revise his estimates upward lest he lose money on the job.

Your numbers are off for most areas. There has been inflation in construction material prices, but that's only one part of the total price of building homes. The other major components include land prices, labor, and permits. So costs could have only doubled from $300k to $600k in areas with very cheap land and permits where materials make up the dominant share of the total cost.

We are refraining from building a deck due to lumber prices. Maybe next year.

Or I buy a mill and cut my own lumber. I’ve got plenty of trees I can take down and use.