What do you mean “unlikely to get a special levy of $200k”? You actually don’t have a choice – the OC has a legal duty to repair and maintain common property. The OC cannot postpone the work because of costs. (So now is a good time to sell up, if you can!). Any owner can to to NCAT for an Order to carry out the repairs. Recent changes to strata law also allow the Dept of Fair Trading to step in and arrange the repairs. In that case the special levy will be raised, and any owner that cannot pay it will have to go bankrupt – or arrange a mortgage to pay it.
So the owners need to get involved. Call a general meeting to review the quotes, and go and get other cheaper quotes that fix the problem from other companies. Strata law requires at least 2 quotes for work over $30k.
But $200k does not seem unusual for a block with several Units. Currently in a multi-storey apartment building a failure of a bathroom waterproofing will cost the Owners Corporation around $30k to repair (current building code requires the bathroom to be stripped entirely, and a new waterproof membrane installed). The Design and Building Practitioners Act applies to waterproofing repairs, and so a design expert will be needed to oversee the work. I’d go with the $200k quote, if you cant get a better deal, as the longer you delay the more it will cost.
(And talk to your bank about a mortgage, or cashing in some of your super!)