There are existing restrictions imposed by the provisions of Pt 4 of the NSW Strata Schemes Management Regulation (2010) with regard to legal expenditure and to the need to obtain quotations, and the NSW Strata Schemes Management Act (1996) imposes restrictions on E/C’s of Schemes >100 lots spending >10% in excess of any budgeted amount, and additionally requires that the Agenda of every AGM of an Owners Corporation (O/C) must include an item to resolve “….if any matter or type of matter is to be determined only by the Owners Corporation in General Meeting.”
That is the means for O/Cs to impose the additional financial restrictions that you envisage – those can be specific to types of expenditure such as on all capital works, and/or be generalist such as to all expenditure exceeding X% (i.e. <10%) of any amount budgeted.
The matters or types of matters that might be considered would depend, amongst other things, on the confidence the O/C has in its Committee Members, but it should in my opinion exercise these additional provisions carefully, lest every nut-and-bolt decision or item of expenditure needs be referred to a General Meeting.