Green Goblin:
CASR does not specify which methodology is to be used. CASA use the oral swabs for a number of reasons.
The urine tests are simple and quick (4-5 minutes and it's all over) but they DO require a bathroom or some other suitable, private place. If a bathroom is used, there is an extensive protocol required in accordance with the relevant Australian Standard.
ALL testing (oral or urine) must be done iaw the AS, otherwise the results are invalid or, at least, not legally defensible if it comes to that. This means if your company sets up in-house testing, your testing personnel must be accredited to collect body samples etc etc etc.
The on site damp only does random testing I believe, not pre employment drug and alcohol testing
Nothing in the CASRs specifies this and as YPJT states, it's a matter for the DAMP organisation to determine how they are going to satisfy the requirements of CASR 99.
As for "pay for your own": common enough in the mining industry, especially amongst contractors.