If you don't mind me asking, what type of beer do you usually brew and how much do you brew at once? What do you estimate the cost to be per 5 gallon batch?
About how much grain do you buy all at once and do the containers just need to be airlocked or kept cold as well? Also, some of the recipes I looked at called for very specific grains.. witbier calls for rolled wheat as well. When buying in bulk, how do you know what you're buying is the right thing?
Well, I brew mostly English styles, and American styles derived from those - Stouts, Porters, English and American pale ales and IPA's, with the occasional oddball thing tossed in there for fun.
The containers have to be just air and water tight - I suppose you want to keep them relatively stable temperature-wise, but there's no need to cool them (I keep mine in my basement, which works out well enough).
Typically I keep on hand a few different base malts (I have been keeping US 2-Row, US Pale Ale, and Marris Otter on hand, but I think I may drop the plain 2-Row once I exhaust my current supply - just not enough difference between it and US Pale Ale). I also try to keep on hand partial sacks (having a group to go in on bulk buys is useful here!) of any Crystal/Caramel I typically use (I have 40 and 120 now, but may switch over to 60 instead of 40 when my current supply is exhausted), similar amounts of Roast, Chocolate, and Black malts, and then usually something to play around with here or there (I've been digging having some Munich on hand lately).
This gives me all the grain I need to make a few of the styles I really like, and if I want to do something else I can typically pick up a pound or three of whatever specialty malts I'm missing.
Similar to what others have also mentioned, I try to buy at least some of my hops in bulk (not as much savings here, but it's nice to have the stuff on hand so you can do an impromtu brew day whenever you feel like it). Note that the bulk hops are best stored in vacuum sealed bags, so there's another up front investment.
I also try to repitch yeast whenever I can - whether you wash yeast to keep it in the fridge for a month or two, or just harvest it straight from the fermenter to use within a week or two, it's another thing that can go a long way toward enabling an impromptu brew day AND save you the cost of another smack pack or packet of yeast.
I typically brew 5 gallon batches, and the cheapest I ever did (a cream ale) came in around $9. Some bigger beers, or ones requiring more specialty malts or hops I don't keep on hand have ranged up in the $20-30 range. As a comparison, I just did a Dunkel with a buddy over the weekend - the ingredients for 10 gallons ran us about $80 at the LHBS. (I didn't have near enough Munich on hand to cover this, so I just bought all we needed for this brew day).