I don't think you're crazy at all. Look at how much other hobbies cost! You could buy a bass boat, a big truck and fishing gear and spend a butt load of money. Brewing is cheap in comparison for how much joy it provides.
I brewed the "legal limit" last year
Cost was $833 in ingredients, not factoring in energy costs (propane, electricity, water). I probably spent a bit more factoring in on-hand grain and hop quantity. That's $69 a month. I usually drink 2-3 beers a night, but have friends over and bring a lot of beer to family gatherings, parties, brew club meetings and competitions. At the end of the year my kegerator was full, six 5 gallon cornies and a 3 gallon cornie with a few batches in primary. If I was the only one drinking beer I would go through a batch a month. I think $100 a month is way more than you'd need when you factor in needing to buy misc items such as tubing, hydrometers, autosiphons, etc.