If the bulk of the outgoing money is settlements, then there can't really be a simple annual average. They probably have some consistent year-to-year costs in keeping non-JW counsel (probably on retainer, if there are enough cases to deal with each year). But legal costs are likely to be all over the place, when you are talking about protecting themselves from CSA accusations or dealing with issues related to policy (eg: Norway).
I do wonder how much of the legal work is being done by lawyers who are JWs and 'donate' their time and expertise. The savings there could be huge, on the order of hundreds of dollars-per-hour for one lawyer. These are probably the ones who write cease-and-desist letters to bloggers and YouTubers, or make DMCA and similar challenges to anti-JW content.