The answer is still build more (which you basically admit yourself in your first sentence).
Homes skew larger and more expensive precisely because it's so hard to build them so developers need to make more money from each one. The fixed costs per unit are too high, so the ones that need to be lowered or eliminated should be. That will incentive building more units not just more expensive units. You'd see a lot more 1200sqft new builds if it was more economically viable and developers could make a profit on a $125k home instead of needing $400k.
Homes skew larger and more expensive precisely because it's so hard to build them so developers need to make more money from each one. The fixed costs per unit are too high, so the ones that need to be lowered or eliminated should be. That will incentive building more units not just more expensive units. You'd see a lot more 1200sqft new builds if it was more economically viable and developers could make a profit on a $125k home instead of needing $400k.