WHY IN THE WORLD IS A PROFESSIONAL RELAXER SO EXPENSIVE COMPARED TO THE $7 OR SO AT THE STORE?

Because "box" relaxers are no good on the hair. Box relaxers have ingredients that u have to mix together because of the shelf-life. Plus a "professional" relaxer is just what it says for professional use, it will be used over and over and over again on different clients it is made with better ingredients and products thus a better product. that $7 one at the store is for one time use only, maybe 2

Because of the word that you said: professional. Now maybe the really cheap ones aren't good but maybe a middle grade price would be good. Now don't get me wrong, i use a 10 dollar relaxer and it looks good if i say so but if you wanted to say start a hair store you may want you upgrade to the higher price relaxers.

Probably because if left on for too long or done wrong you can lose hair and damage it so it's expensive because they constantly monitor you to make sure ur hair isn't damaged or worse.

You are paying for their time and expertise, also pro grade products (sometimes).