How do I find a criminal lawyer I can pay after he wins the case?

You may find many private attorneys that will work with you on a payment plan-but I would be wary of any attorney that would enter into an agreement such as the one you are suggesting. A criminal defense attorney has a duty to investigate a case that is independent from the State/Federal Government. When you retain an attorney you are paying for that attorney's time to conduct the investigation, research the law, review the evidence and render an opinion as to the possible outcomes. No attorney can guarantee a "win." No one can predict with entire certainty what a Judge or Jury will do. I think that the question you should be asking yourself is how much is your fiancee's liberty worth?