You're not the first to state this!
It's obscene how these suppliers are guaging the service. 
Foo
I've had OT's mention to me that I'm a quayer of the cost as well known local Deliverers, in installing products.
As I understand things, there are only a couple of suppliers of eg, hand rails modular or prefab, so the costs are roughly the same for all installers.
The cost of installing is where huge cost to the taxpayer is.
I may of mentioned here before this.
I have been told that house cleaners, they don't even use their equipment or products are charging the NDIS @ %120 per hour.
This seems to be an exceptable price to pay within the industry.
I doubt they would have public liability, I could be wrong.
They haven't completed an accredited course. Eg trade, apprenticeship or equivalent.
Don't carry 30K worth of tools.
You would think they would have completed a Police check/working with Children. ABN.
Anyway, the system IMO is broken, but nobody wants to know about it, except to blame someone else.
You don't use magic to disappear, ya use a 4x4 & Swag.