So far we've been able to keep our costs fairly modest, but as the case (now cases) go to trial the costs will likely balloon rapidly.
It's always a concern though because support might stop at some point, especially since the total cost is more or less unbounded. For example, in the defamation lawsuit against Peter McCormack his sponsored pulled out after the funds expended crossed a million UKP sticking Peter in the middle of some complex and expensive litigation and forced to withdraw most of his defenses because he couldn't afford the cost of them.
Fortunately, at the 11th hour he was able to prove that the claimed damages the case rested on were totally fabricated (the plaintiff claimed to have been dis-invited from academic conferences; McCormack got a statement for the organizers that Wright's submissions were rejected by peer review for being rubbish), resulting in McCormack ending up with a 1 UKP judgement against him ... plus some 900k UKP in legal costs (which he's currently fighting to get dismissed).
A challenge future fundraising may face is that the time-scales of court are not compatible with the attention span of the public-- the number one thing I hear when I have updates is "oh, is that still going on?". The second most common is "that guys a joke-- just ignore him, he only wants attention". Well, I wouldn't argue that he's not a joke, but even a joke can cause tremendous damage especially when everyone's reaction is to ignore it.
The opensats fundraiser was able to raise about $1.5 million dollars for hodlnaut's defense, which on one hand is a tremendous success--- but on the other hand is about an order of magnitude too low. Which is why I'm attributing problems here to the legal system and inadequate protections of open source licenses in light of them (MIT's waver of liability is arguably stronger than most too) rather than saying the community hasn't stepped up in support.