If you're in Sydney or Melbourne, get ye to Binocular and Telescope Shop (BinTel) and have a conversation with them. If you're elsewhere, call them and they may be able to point you to other places.
If you can, also get to an observing night (which aren't as common here as in the US) so you can find what you should expect to see. People there will be happy to show you. They were all in your position once.
The reason the scope looks small in the Nat Geo shop is because a lot of that money is paying for the tripod and mount. Ask the folks in the telescope shop to show you their Dobsonian telescopes. With a Dobsonian mount, you get more scope for the same money because the mount is sturdy yet very simple.
Ask also about introductory books. That will also give you an idea of what you might see, as well as some perspective of what you'll be looking at. Most galaxies look nothing like they do in photos, for example. One thing you'll learn is HOW to observe and learn what you're seeing.
The best advice I can give, though, is to get first-hand experience of looking through one.