I agree and love my (Lfs) but I have a family budget too.
If I want [insert product]:
My (lfs) sells it for $[higher price] and I can get online for $[a lower price] with...
You don't have to explain anything – most of us have a serious budget (I think, right?) and it's the same economics everywhere and it's been going on for a good long while now. (It's where all the LFS's have gone.)
The online guys have volume so they can sell at a loss or near-loss
to take business away from your store and still make
good money on the year. (Don't think they're doing it just to give you a deal.)
It's well worth pointing out that most items the online guys sell aren't such a great relative bargain as the one you point out – salt is about the best deal they offer. Usually online is only better "on average" if and only if you can get them to eat shipping – and not always then.
Your store also doesn't gouge like that on all items, so you've really cherry-picked your example.
If they do, you should open a store of your own as it would be very easy to outcompete them. (I have a little experience on this side of things, not just speaking blindly.)
We should also all remember that the LFS
is run by our neighbors – not by some anonymous Apache webserver like the online guys.
If you think they're really doing a bad job with their pricing consider talking to them about it in a completely non-emotional tone.
$74 is not good for a box of RC, but it may be due to the price they get it at, or they may not know better, or they may not know there are other suppliers, etc.
Don't be so cut-throat against the LFS on prices.