I have a 2 litre hydration pack that I use on hot and longer rides. It is not camelback but just same type of bag. Cheaper too. At least when I got mine.
http://www.mec.ca/product/5032-787/m...q=sac%2Bgourde

I still prefer the bottles now because the pack is "heavy" to have on your back, it does not let air circulate between skin and jersey and the "wobbling" of the water in the bag gets annoying. But I find it useful when doing longer runs. I don't like to ride without hands on the handlebar even for a short time so this is easier for me to get a drink a I clip the hose near my mouth and when I want a sip, it is just a second away.

The fun thing is the bag although small, is roomy enough to put a few things in there also like arm warmers or snacks, etc.

You have to try a few models to make sure you are comfortable with it on your back, and front.