For an average beer (average hopping rate and average ABV), I'm usually right around $30 for a 5 gallon batch. That's everything factored in, from ingredients and water to propane, shipping costs, cleaning and sanitizing, and all miscellaneous items. I brew about 20-25 batches per year. So, about $750 on the low end.
I don't brew from December through February, unless the weather starts getting nice again early, as I'm not fond of brewing in the cold. This also helps keep brewing from conflicting with the holidays. During this time, I get a good idea of what I'll be brewing over the next year. It always changes, but I end up brewing about 75% or more of what I laid out. In February, I'll order a boatload of hops from farmhouse brewing supply - several mixed lbs of hops, totaling about $150 shipped. After that, it's rare that I buy any more hops through the year. I buy base malt in 50 lb bags from a local brewery at $30/bag, and typically go through 4 or 5 of those per year. I then plan out 4-5 beers at a time and order all specialty grains, yeast and extras i need at once to save on shipping costs (no LHBS here). So, 4-5 orders per year there.
I'm gearing up right now to start a frozen yeast bank, which will dramatically cut my yeast costs. From roughly $8 per batch, to maybe $.25. Factor in DME for starters, and it's probably $1 per batch. Will have to wait and see.
I buy RO water from the grocery store at about $5 for 10 gallons. I build my water profiles from scratch and have enough breweing salts to last years, so that cost is negligible. Propane is roughly $20 per tank and I get 4-5 batches out of one. Whirlfloc and yeast nutrient is approx $2/batch. I estimate C02 at $1 per batch.
In the summer when ground water reaches high temps, I hook up a pre-chiller in an old bottling bucket with a 20 lb bag of ice, which costs about $5.
I mix 5 gallons of RO water ($2.50) with Starsan ($.50) in a 5 gallon Lowes bucket and that typically lasts through 5 batches, until it either gets low, gets cloudy, or begins to collect a lot of junk in the bottom of the bucket.
I approximate PBW by mixing OxiClean free with TSP-90 at a 3:1 ratio. Oxi is about $7 for 3 lbs and TSP-90 is $12 for 4 lbs. So I get 16 lbs of cleaner for $40. Not sure how that breaks down per batch exactly, as I use that cleaner on my beer glasses and other things. I think I go through about 8 lbs per year.
Long story short (heh), while I actively look for ways to cut costs, I buy what I need, when I need it. I don't have a budget at all. Hopefully in all my rambling someone picked up some tips to save money.