Unfortunate news. Prefab seemed like such a great option – but I have heard a couple of stories to back up your claim. We just built a house out of SIPS, and prior to having it built, we talked a prefab company and there was no way they could build an existing design for under $200/SF – at least the one we liked would be $250-300. They priced out our design too, and they claimed the cost would be about $200, but too many things were not accounted for (like anything we could get locally, and they didn’t exactly specify what mid-high end finishes would be). Although we chose to go with SIPS for a lot of the right reasons, we figured it cost about 20% more than conventional stick built — so not necessarily an immediate cost saving.