An addition-renovation with a crawl space is the most common type of addictions. It is not quite the cost of a basement style but is more expensive than some other style with no full foundation. Excavating and masonry elements are still needed that drives up the cost but is considered by most to be the standard in foundations. After all the same approvals as a basement style are achieved, i.e, zoning, surveying, contacting I-800 dig to do a full mark-out for any buried obstacles. We can excavate for a footing inspection, pour a footing and have it inspected, lay block or pour concrete foundation also needed to be inspected, either pour a rodent slab or clean stone with a 6 mil poly vapor barrier, which also needs an inspection. After successful inspections, we can move forward with the framing. With the new energy codes, the insulation requirements have gotten demanding. Instead of R15 wall insulation it is now R19 which means the studs need to be 2x6's instead of 2x4's. The floor and roof insulation has also been upgraded to R30 in the floor and R49 in the ceiling. This increase in the roof insulation has greatly complicated new addition type renovations when a vaulted ceiling is in the plan. If the addition-renovation calls for a vaulted ceiling, different types of insulation are required to get the R value. By the way these types are much more expensive than the old standard fiberglass R30 batts. As you can see there is a great reason for construction costs to skyrocket. In addition-renovation materials have tripled since 2020. Construction materials, labor, and transportation have dramatically increased. Also since covid, production and availability can not be cost dramatized enough. All other supplies, i.e windows, door, lumber siding, roofing fixtures, appliances have skyrocketed. Don't think the builder has no justification for the money he has to ask for construction.