I am not a lawyer, but .... you might look for an attorney who'd be willing to review the case and, if s/he found it a meritorious claim, agree to take it on a contingency basis ... if you win s/he gets 1/3 (or whatever you agree to), as in personal injury cases. Or, there are a few statutes that require the losing party to pay the winning party's legal fees and costs. I doubt that would apply here from the little info provided.
However, even in contingency cases, the client usually has to pay expenses ... regular administrative things like copies and postage/messengers, etc., don't come to that much, but depositions and expert witness fees are steep. You will need economic experts to determine the market value of your share of the LLC.
Your former partners would likewise have to hire an attorney or attorneys and face all the court costs and expert fees ... so it would be in their best interest to discuss buying you out at a reasonable, mutually agreeable cost. Litigation can take years and just wears out everyone's resources. It should be avoided if at all possible.
I would be hesitant to proceed pro se, but if that's your only option, you can find the Rules of any US District Court online. Same for most local courts.
I think US courts require a minimum value to the case of $75K. The filing fee is steeper than most local courts, around $350 or $450 (can't remember.
Think long and hard about this (within your statute of limitations) because you might be better off taking this loss and just getting on with your life. If you are young, especially, you can rebuild your life and credit in time. Probably in less time than it would take to litigate.
Good luck.
Thank you.