I have a question, just because my gpa is 3.4 , the EOF, the program that i'm in, invited me?

to be in Chi Alpha Epsilon Honor Society, i want to know is this a sorority organization?, what do they do? , what if i don't want to join, they told me i have until march 25 and pay $70 . is this a choice, because i don't to do anything or join anything that involve sorority or anything in that organization.