My own account:

We have around 15 snakes now. We probably had around 10 or 12 when my WEEKLY feed bill for buying live rodents was $50. That's $200 a month, $2,400 per year. 30 minute round trip to the store, an hour and a half "shooting the breeze" with the shop owners. This is when I made the jump to breeding my own.

Now, I am going to round it up generously, I am spending $50 a month, $600 a year. Initial cost for my 6 bin rack was about $150 if I remember correctly. I try to keep my breeding to a 1.3 or 1.4 so I only have to clean about once every 5 days and that takes 30 minutes. Daily care of feeding 1x a day and waters every other day, takes less than 10 minutes.

You are going to be spending a fair amount of time with your rats on a day to day basis. This is why you don't necessarily need to be in love with your rats, but at least like them. If you are on the disliking end already, be sure to get good stock that are not aggressive and that don't run and scream when you pick them up. Nice rats are a lot more pleasant to deal with than the skittish ones.