I actually had a semi fight with the mrs about this subject on the weekend. After only 6 weeks of brewing, I've made quite a lot of little purchases, not hiding any of it from her. She finally confronted me about how much this hobby has cost us so far, why not just buy beer? I said it's probably cost less than just buying beer, and she said it's not possible.
Well, now I've done the numbers, and the only beer you could have bought cheaper at the same volume is 30 can slabs when they are on their best special at Dan Murphys with a 5% discount. In the mean time, I have brewed 5 different types of beer, including an all grain, and have all I need (but still want a lot more) to make K+K, AG, ferment with temperature control, and bottle my beer properly.
Ongoing from here, without buying in bulk, I'd estimate $25 for a coopers kit and all accessories for a 5% ABV will make $85 @ slab prices, and $45 AG will make around $120 @ nice beer prices. Can't easily be argued with.
For now, I will continue to spend on things as I see fit. We'll see how long it takes her to question the costs again, at which point, I will at least have the answers she won't like.