As roux said there are a bunch of variables that will determine if it's worth it for you.

The first being the price you can get frozen feeders for and availability. Some people don't know any better and will happily pay full retail price from places like petco. Others are use to buying online and just paying the shipping. You mentioned you have local shows and can get frozen cheap. Some people don't have the local show option.

Second consideration is to plan what size feeders you may need in the future to feed your herp. Obviously you don't need 100 frozen pinkies for a snake that will be moving up to fuzzies in the next month. With breeding you can retain the feeders till they are the size that you need.

Another consideration is initial investment in getting set up for feeder breeding. One person might be able to scrounge together most of the required things like water bottles, caging, and even the feeders for free. While the next person might want to go out and buy all new stuff from the pet store. Yet another person might decide to build a rack system for their feeders.

The deciding factor for me was when the number of snakes got to a point that you could keep a happy ratio of mice to snakes. What I mean by that is you don't need a colony of 1.3 feeders for one snake. That one snake will never be able to keep up unless you euthanize/freeze them. A 1.1 colony of feeders for 4 snakes would be putting a lot of stress on the female since she will be in constant production but the time between births you will still be buying frozen feeders. I'd consider the happy ratio of having enough snakes that can eat a litter of feeders a week, and having enough feeder colonies to be able to produce a litter almost every week or two. That's kind of where that number 10 comes into play (estimated average litter size to feed each week). The more snakes and feeders you have the more wiggle room you have incase you get to heavy on the feeders you can slow production of feeders or feed off some of the feeder/breeders.

Some people also just like having control over what they feed to their snake.