Howdy mspoker. Simple question for sure, many players can certainly say little to no money was invested to become a winning player in the case of building up a br from nothing playing in the freerolls
Some perhaps, like myself unfortunatly, have over the years invested and lost way too much before realizing its time to give up on the tilt and simple focus of regaining lost funds (as just caused a deeper hole to get out of) and focus on a grind to improve their game and hope that some day to get onto the track of being a winning player.
I have a long ways to go to be a "winning player" by all means of the word, I play a good game when I play a good game but in the past let losses tilt me too much that I would spew and donk to try and get back to even. Not a good approach by no means, sure could be some stories out there of it happening with taking xx amount to xxxx amount in a session but again its the risk of going further down.
So long story short, you don't have to invest any money to have a learning period or at all if you can play through freerolls and build slowely. Volume is a great learning experience as well as being active and getting feedback on posts from forums such as cardschat.
Good luck on the felts and your learning experience.