The price varies depending on your home country Alex. I don't know where Natedogg is from and it does not say on his profile. It varies because of what the insurance company can expect to be able to get from your national coverage. ie. If you are a Brit, will the NHS pay to repatriate you on an air ambulance.
If you go to the WN website you will see the first question asked is where are you from. Enter the UK and ask for a year of level 1 coverage and the price is 207 GBP. So I don't see where you are getting the 1000 for 2 years from. You cannot ask for more than 18 months initially with WN so I can't give you a 2 year comparison. For 18 months it is 437 GBP. I can't see it getting to 1000 for another 6 months given the 12 and 18 month prices. It will however be more than your 280 GBP price obviously. But can you extend if needed?
What I suggested to the OP is to start with 6 months coverage (since they allow you to extend while 'on the road'). That would cover the time period up to his getting to Australia and if he found work then he could decide what to do from there. Extend coverage or rely on Australian employee coverage if it were provided to him (not all jobs backpackers take provide health cover). For 6 months WN wants 113 GBP for a resident of the UK.
Using your own scenario of employee coverage in Australia, that is all the OP might need to pay for, 6 months coverage. Why pay for more unless needed and assuming you can extend? Extend or start a new policy while 'on the road' is something that a lot of travel insurance providers do not offer. It can be very important if your plans change in some way. Don't underestimate it.
You can even cancel the remainder of a WN policy, receive a refund and then at some future date if you go back on the road, start a new policy from OUTSIDE your home country. See where that might come in handy?
There is more to consider than just price.