This probably includes the amortized costs for taxes, electricity and other services used throughout the week when it sits empty, probably also paying off the 'loan' from the society who funded the construction.
There are no taxes and there are no loans. The society owns these assembly halls. If it loaned itself money to do so, and is making the rank and file JWs pay it back, that's criminal.
There is electricity and there is water and there are supplies like paper products, gas for the lawn mowers, shovels for the snow, etc. That's it.
This isn't just suspicion. People who have worked in accounts at assemblies have confirmed this. The announced costs are NOT actual costs. They are projections based on a certain amount per publisher per day and they are highly inflated above what any actual costs might be.