Advice On What Bike To Purchase

Hello,

Need some advice on what bike I need to get. I am a runner and would like to transistion to doing duathlons. What bike is best. I know both mountain bikes or road bikes can be used. I am barely 5 feet tall and I really don't want to spend more than 1K. The less the better but i also want it to last. What brands are good for someone as short as I am.
Giant? Is this any good as a starter bike> http://pacbikes.com/product/giant-defy-5-211600-1.htm?utm_source=Giant%20US-BuyLocalNow&utm_medium=BuyLocalNow&utm_campaign=BuyLocalNow&variations=1087392,1087393&buyLocalRequestId=2347512
or a Cannondale (do they even make anything under 1K)?

Any advice is greatly appreciated.