We actually don't know if Monty had pro bono representation. A popular theory here was that Schneider was working at a deeply discounted rate, but that's just the usual thread speculation. Nick himself said that he thought Schneider was working on contingency, but Nick's opinion means even less than anyone here.
What we know is that, when it came to the appeal, Monty had to raise money to bring in a guy that specializes in appeals (meaning that very definately wasn't pro bono). He out-raised Nick... and then... beat Randazza with a much cheaper lawyer. Cue Cokestream.
It would actually be pretty funny if Monty's total outlay for this whole thing is pretty insignificant and, in return, he caused Nick to burn hundreds of thousands of dollars, and get so fucked up on coke on a livestream that the 5-0 noticed and included it in a search warrant application. It would still be a Nick W against Monty, I suppose, but a really pyrrhic one.
It also makes one wonder what would ever happen if Nick pissed off somebody with less baggage but more money.