What is cheapest Mac Book I should get?

I'm in the market for a Mac Book to replace my old Windows laptop. What is the cheapest Mac Book I should get to use primarily for image storage, viewing and limited editing using Lightroom 4.3 (and rarely Photoshop CS5) while I am traveling?  I plan to get Apple Care. Should I get it through Apple or get it from one of the less expensive resellers like B&H?