Roughly what would be the cost of an external aerial to pick up all the digital channels?

Supply and install?

Supply only? Are they easy to install yourself??

I rang a few places before getting mine done, all around $400 with 3 points, fully installed. That's possibly including Perth Tax, I'm sure prices will vary from state to state.

Should have said I am in Sydney.

Does the 'including points' mean doing the wiring to them all?? We put a heap of coax through the house before plasterboard, so would only need the first inital point then I would imagine we would split it from there?

Yes, a point meaning the actual aerial socket in the wall. So the price included the aerial, a 4 way splitter (1 empty for future expansion), all the rg6 quad shielded cable and the wall plates.

Installation was slightly easier as I had conduit and blank wall plates installed during the build so the installer didn't have to go fishing for the cable nor do any messy drilling.

Sounds like what you need should cost considerably less.

I got Mr Antennaes or something like that to fit one last year, in Brisbane. Was under $300 supplied and installed with them running rg6, down the wall, wall plate and tuning the telly in.