The $229 million figure isn't the build cost - it is the estimate of the total economic activity generated by the project. Probably a bit high , as these benefits invariably are exaggerated when a large capital project like this is announced in order to encourage the planning officers & local council officials. In reality , there will be very little economic benefit to the local community other than building material supplies companies - the result is a gated community with very little spend generated for local businesses during construction or operation. The WTBTS says that only 25% of the work is done by paid workers , with 75% by volunteers.
Even so , a huge long term project for an organisation which has claimed (for 140 years) that Armaggeddon is imminent. As often stated , the MO of the WTBTS is -
Step1: Buy land (with donations) , build (with donations & mainly volunteer labour) , use for a few years , sell on at a huge tax free proft.
Step 2: Go to step 1.