I would speak with the manager of your local grocery store an explain to him/her that you are looking to make a bulk purchase. You would like to support the local store (this one) but you can't justify the higher price for bulk purchase. Explain that you were planning on doing a longer trip to buy "said" supplies, but thought you would see if they could work out a deal with you. You buy at the local store, if you can get a good discount!
Most stores will work out a deal with you. They would rather make less on the purchase than loose your business.
Come prepared with your list of things and find out what Sam's or Costco would charge. Then when they make you an offer, you can explain that "yes" you like the offer, or "no" the price is still to high. Give them a chance to come down one more notch in the price point.
Once they realize how big of an order you are looking at - they will most likely accommodate you.
Bakeries are another good spot to look. You can ask the baker if they might order some extra for you. They might be able to give it you for a little over the wholesale price.
You could also see about getting together with local families and starting a food coop. Some distributors are happy to sell to food coops, just like stores. They most likely will require a minimum order. The food coop pricing is usually slightly higher than wholesale, but tons cheaper than retail.
The Emergency Essentials site sounds good too. Right now they appear to have free shipping on orders over $199.
http://beprepared.com/default.asp?bhcd2=1288032526
Can't argue with stuff shipped free to your door!