If the strata manager has breached the terms of your agreement (with them) and this is not an emergency, and there is a cost attached to halting the work, you may be liable as they were acting on your behalf but then you can try to recover the money from them because they were acting without proper authority.
Remember that, apart from insurances, the strata manager is not legally obliged to get more than one quote unless specifically instructed to do so or if your scheme is “large” (more than 100 units) and the cost exceeds by more than 10 percent what has been budgeted for in the annual financial plan.
And I have just realised you are in Canberra … maybe PeterC can offer more accurate advice.