The exorbitant "hazardous materials" shipping fees kill any bargain prices I ever find on mail order ammo
Not sure what you mean by that, but ammo doesn't require haz-mat fees (primer and powders do - though I've heard that is set to expire in 2014).
All in all though, it depends on your local options. Online doesn't beat my local gunshop by $1 a box - they typically beat them by close to 50% per box (no lie - the cheapest I can find 9mm Makarov locally is $22/box). Heck even Wal-mart wants around $17 per box of 50 .32acp around here which I can find for $12/box online. Figure that in and as long as you're buying more than 4 or 5 boxes at a time, and its cheaper to buy online.
Only thing I do buy locally (always) is powder and primers. They're still overpriced, but the $25 haz-mat fee (in addition to shipping) really does make it hard to make up unless buying in great volume. If their haz-mat status DOES expire in 2014 though that will certainly change.