Lowepro’s DSLR Fastpack AW line is awesome and just got even better with the redesigned AW series. I have had two Lowepro bags in the past and have loved them both. In the AW Fastpack 250 you can fit multiple lenses, your laptop(up to 15″) and plenty of other gear you need for on the go shooting. I have also used the Slingshot which is ultraportable. For longer trips I would stick with the larger 250 but the Slingshot works great as a day pack when you don’t need your laptop or more than 1 extra lens with you. The 250 fits comfortably under your seat on flights and has enough storage for a water bottle, couple of books, laptop, and some snacks.
You aren’t saving anything by going over to Amazon but its a great place to get some reviews. The best way to save on this is is to get a used one on eBay. I saw a 250 for for $33 last week and it was in great shape. And if you are like me and like to try new different bags all the time there is no need to have a brand new one.