Not an architect or construction worker, just someone with too much free time, but light research suggests that overall project costs are generally lower for structural insulated panel (SIPs) buildings in a lot of places despite the higher material costs because:

1. lower construction labor costs (decreased framing labor, smaller crews needed)
2. faster project completion (pre-fabricated parts)
3. higher energy efficiency (typically much higher heat insulation and much lower air leakage)

Of course costs depend on where you live and complexity of the building, but total life-cycle cost of a SIP building can be as low as half comparatively.

You can read some articles/papers if you want [1] [2] [3] [4]