However, they increase in a 2500sq ft house is probably $8-15K. It is NOT $100K. something else is up.
I think the increased cost is only part of it. Another aspect may be that they know they can get a lot more for it now, so they are happy to undo the deal that they entered into several months ago.
All the lumber in a house does not add up to what the furnace/AC costs. The big money in a house is the kitchen.
Windows and doors cost a lot more than lumber, plywood, osb.
FYI, the wholesale lumber market topped out a couple weeks ago. Plywood/OSB is still tight. Prices are just starting to come down. For example, the price of a 4x4-8’ #2 SYP from a sawmill went from a low of $350/mbf in March to a high of $1400/mbf last month. We can buy them today for $850/mbf.
2x4-16’ #2 Spruce was $400/mbf in March. Topped out at $1500. Today they are asking $1150. Prices are falling. They do not fall equally. Just like they did not go up equally.