I usually buy local. As previously stated, I want to support my local businesses. I'm probably paying a little more, but I'm not exactly scraping by.
I think of it as making an investment. If I decide to brew in a whim, or I need something quick, like an airlock or sanitizer, I can just stop by and pick them up. Also I'm a sucker for the free shipping trap (If you spend x amount). If all I need is something small I probably end up saving money by not filling my cart with extras just to save a few bucks on shipping.
All in all, I feel that if I support my LHBS (investment), they will be there to support me when I need it (return on investment.)