If you only count the cost of ingredients it is much cheaper to homebrew. That said it takes a really long time to recoup your equiptment costs and even then as you get more into brewing you tend to purchase more toys. Such as when you do All grain brewing you'll need extra equiptment. Plus if you're like me you'll end up giving away so much homebrew because friends are interested in how it tastes and after they taste it they like it and want more to make brewing cost effective.
I usually have about $20 in the typical 5 gallon extract batch. All grain batches a little less maybe $15. The key to saving money is purchasing in bulk, but obviously you need to store excess ingredients properly. Extra hops double baged in ziplocks in the freezer for example. Liquid extract is much cheaper in the 6lb containers (half gallon jugs) than in the typical cans, but in the jugs it should be refirgerated.
You'll probably be money ahead by brewing yourself eventually, but don't count on it happening soon. You will enjoy the process and the product though.