Depending on the quantity you are going to be using, and your location (i'm going to assume Australia), you are going to want to check a few places.
1) Local Electronics Stores - often have hit and miss selection, and the prices are terrible, but they are quick.
2) Digikey/Mouser - They are going to be the cheapest (especially in bulk), and have a large variety, however I'm not sure how their international shipping is. ( http://www.digikey.com/
) & ( http://www.mouser.com/
3) Sparkfun - The most support, and great for finding sensors, prices are decent, and selection is fair. https://www.sparkfun.com/
In terms of the prices on the site you listed, they seem on the high end of what I have seen elsewhere (then again I'm not up-to-date on the strength of the AUS Dollar)
Hope this helps!