That is a tricky question. If you don't have enough adult females you won't be able to sustain your colony. Too many and you end up with a lot of extras (which you can sell, but not get rich on). You have to go with having more than not enough to do it right. It also helps to do a little math to figure out what you will have after 4-5 months of waiting. Figure each female will produce 30-40 babies a month with ideal temps, humidity,food, and a correct male/female ratio . I have colonies with 200 females for each. Each colony produces around 5,000 babies a month. I wouldn't start with a colony with less than 200 adult females. With the effort, time, money, and determination you begin with you don't want to be disapointed 6 months later by wishing you had more. As time goes by you can decide if you need to downsize. It's easier to do that than to start building a colony up again.
I all comes down to money and time. Pay a lot, have a colony producing sooner. Pay little for 1/4 ones, wait 6 months for them to start producing and wait another few months for those babies to grow. $100 seems like a lot of money for that many sub adults.