If I were building this new facility in the real world, which is what I do, here's how I'd throw together a 5-minute estimate:
1) Site work is intensive. Lots of clearing. Lots of removal of existing buried utilities and storm. Huge buried detention system (very expensive) in lieu of detention pond. Site grading. Building Pad @ 12,500sf. New storm and other utilities. $750,000 - $1,000,000 site package, easily.
2) The building, built to Disney and Florida standards, will likely be structural steel wrapped in concrete or masonry with a flat rubber roof. 12,500sf @ $150/sf = $1,875,000 for the building shell, with major mechanical systems in place and electrical service to the building.
3) If built out similar to PFTH, it's a lot of standard office-type construction, with magic stuff added to it. Build-out of an interior retail/office space is $75/sf, so $937,500 to build out the interior, plus probably $500,000 worth of magic (scenery, show lighting, controls, security).
4) Whatever exterior scenery they put back. If just trees and landscaping, maybe $50,000. If rock work, $200,000.
5) Hardscape is probably another $75,000.
6) Parking is another $75,000
This comes to about $4.66M for the building and related site work, using all the worst case numbers. I'm sure we can add a 20% Disney cost inflation to that.
The new building is not indicated as being modular. The reference was to the existing modular storage building that has to be torn down and moved to the east end of this lot. It will be out by the service road.