I don't think Costner is one of these guys who has Brad Pitt money of $500M or more.
Yellowstone was usually only like 10 episodes, and I think 5 seasons so far. Take out the commissions and other deductions, and tax, and it's not the crazy fortune that $1.3M sounds like. (Also, I'm sure he wasn't making $1.3M in the first season). But let's say he was and it's $65M less probably 25% in payments to reps, leaving $48M-ish, and then tax will take that down to like $24M, and he'll argue he spent a sizable chunk of that on the family over the last 7 years or whatever that it's been on.
The wild card is what his back end is worth though, as Yellowstone is a phenomenon (even though it has been shit since season 3), and he may even have a piece of derivative Taylor Sheridan projects since he was on the first/flagship show. But I wouldn't be surprised if Paramount is screwing him and reporting nothing special in the form of profits just yet. I actually did a deal for a client for a show within the Yellowstone universe, and they are incredibly stingy and barely move from round to round of negotiations, though I became pretty good friends with the lawyer on the other side during it (and have asked about Costner's deal in conversations, so know a bit in terms of magnitude, and not details, off the record).
Anyway, the point is, Costner isn't insanely wealthy like Clooney, Pitt, Damon, Bale, and others who had massive paydays during the heyday of the $20m plus per picture era, and was pretty dormant for much of his 18 year marriage until Yellowstone. I'm sure he's got investments and made a shit ton on stocks and real estate over the years if he had decent reps, but all of that stuff is separate property has nothing to do with the marital estate. So, I would guess there's zero chance of any $30M plus payday for her. I would guess she comes in more at $7M to $10M cash, plus the alimony until the kids become adults. Which is nothing to sneeze at when there's a perfectly valid pre-nup that the court will be happy to piss on.