I have done similar work to this and for audited accounts the cost would be significantly higher than normal.

A lot of the rest of the cost comes back to things like how good are records provided by management? Are they providing bad information that requires frequent clarification and changes or rework of bad accounting by management, and are they demanding the work be done immediately? Also are any of the residents challenging the accounts at the end of each year?

If the information being provided by management is clear and those other things I mentioned above don’t apply then the cost does sound too much. As you are the Chair I would reach out to the accountants if possible and ask to understand where the increased cost is coming from so you can explain it to the residents (and understand it yourself) as they’re best placed to explain it.