I tried the breeding thing for a while and it was successful, at first, with some Lake Tanganyika africans and ancistrus'. I bred common fish, but always had some local buyers lined up.
I had 15 tanks set up in my basement (10, 20L, 40, and 55 gallon tanks) and bred smaller fish, some in community type setups. The profits payed for my equipment. My apartment includes free water, so doing frequent, sizable water changes (as required for breeding) did not incur an additional cost to me.
When winter came however, the additional electricity needed to heat the tanks reduced profits that I made. Shipping in Upstate NY is tricky as temps can vary as much as 50 degrees in the same day int he fall and spring. By October I had started dishing out additional money for hand warmers and insulation supplies.
I then lost two shipments in a row, and lost nearly every penny of profit I had made in 3-4 months. When the local buyers stopped buying my stock, I found it more difficult to get rid of the fish I had. I eventually sold my adults, sold a lot of the equipment, and went back to keeping fish for fun.
In hindsight, the amount of time needed to feed the fish and perform general tank maintenance hardly made it worth my time. With 15 tanks I was doing water changes daily. If you factor in electricity for all the pumps and heaters, as well as the cost of food, I doubt that I actually turned any profit at all.
I now have only 6 tanks, and I breed convicts (for feeders), ancistrus, and some cyprichromis (always a market locally for those).
Getting the job at my lfs is a dream job for me plus the discounts and being able to order items for myself when the owner makes his order every week. I am sooo excited. 
