I am usually around $30 a batch. Varies from a simple blond to DIPA. Grain really isn't the expensive part, its the hops and yeast, candi sugar, spices, fruit, etc that add up. $2 for dry yeast or $7 for liquid, 5 dollar difference in a batch. I usually get hops around $2 an oz. try and pick things on sale or cheap, occasionally will buy a pound.
Buying a 55lb sack of grain will shave a little bit, washing and reusing yeast, buying hops in bulk. I think 15-20 dollars is about as cheap as you are going to get for an average 5 gal batch. You could also look into partigyle brewing, spend a little more up front, but get a double batch.