well 3" is the break-point for cost. you can do less than 3" of lift just by adding or replacing a few small parts (coil spacers, shackles, etc) or by spending a little more for better springs (such as the OME kits). once you get up to 3" then replacement springs are mandatory, steering becomes problematic, and control arms get to such angles that ride quality suffers, and so forth, which adds up to hundreds of dollars pretty quickly. a lot of aftermarket parts are sold for 4-6" of lift, so 3" is also kind of a no-man's land on heavy duty parts.
2" is a nice boost over stock and won't affect your stock gear too much, otherwise go to 4"