Hi Shelly1.
We have sat access via a Globalstar sat 'phone, but it is slow (less than dial-up) and costs $1 per minute, so we don't use it, but could in an emergency.
We use a Telstra NextG wireless modem which is quite fast and works anywhere there is NextG service. Our plan is $49/month (200mb) or $79/mth (500mb) which is not cheap, but very convenient and includes the modem.
Better plans might be available via Bigpond, and "relocatable" plans are cheaper than "mobile" plans. You need to suss them out at the local Telstra Shop. Don't let them tell you what is best for you until you have investigated very thoroughly.
It is also possible to use some mobile phones as a modem, but it depends on the plan you are on how much this costs.
If you want good coverage, you must have it via a Telstra NextG service. No options.

Cheers,
Peter.

We use vodaphone mobile net $39 pm on 24 mth plan 5 gigabytes download.
Where there's NextG coverage it's excellent, where there's not it's very slow or non existant.
Most van parks we've found have either free or prepay wifi access.
If your'e not running a corporation from your van you should find you'll manage quit well.
We have found a way to do our blogs offline then post them when we hook up.