If the expenditure is identified on the budget for that committee, the authority should really be with the committee to spend that money on the item in question. Model financial regulations do limit the amount of money committees can spend - in our case, all expenditure over £5000 has to be formally approved by Full Council. All payments have to be presented to the Full Council too for approval which is a second line of monitoring spend.
There is always risk but checks and balances should be in place in order to mitigate it.