What is the likely hood of getting a mythical via regular cases?

i have 352k credits saved up and im probably going to save up another 300k before i buy cases. But i do not understand the math to it because it says i have 132% + luck increase yet im still have not gotten one. I was wondering what was the most someones spent trying to get ahold of one.~ i just want to set my standards higher than necessary so i dont get disappointed