That $210 buy-in mentioned in the OP sounds like a lot. But if you average the cost of a book set over the length of a campaign, the $/hour is pretty good.
But that's not quite right, is it?
Because I think it's relatively uncontroversial to say the vast majority of TTRPG books purchased
don't get used for actual campaigns, thus dropping $210 is a much bigger issue than it would be from a $/hour perspective (which to be clear, is an sketchy metric, so let's not get too deep into it) if there was certainty. Certainly I wouldn't get into a niche RPG like Starfinder 2 for $210. Like, no way.
Also, we're discussing hardcovers and so on, which are
@Morrus outlines are unprofitable, with thin margins or are actively loss-leading. But is that how most companies make most sales revenue (we know it's not how they make most profit)? I mean, I don't know, I genuinely don't, but I'm presuming not, because personally I have over the last 10 years about a 50:1 Digital:Real book purchase ratio, and I know for a lot of other people, it's at least 5:1, and many people purchase both the physical and digital versions of books (sometimes multiple digital versions). Which is presumably how the business keeps running at all!
For me the price limit is dependent on a number of factors, it's quite flexible:
1) How likely am I to actually run/use this RPG/RPG product?
If this is low, then the price limit goes downwards rapidly. Like, I bought Daggerheart digital because I didn't expect to actually run it. But after I had run it, and it was a big hit, I bought the physical copy.
Starfinder 2, for example, the odds of running it are low at best, so the idea of dropping $210 on it sounds insane to me. It seems to me like Paizo have been very self-indulgent in the format they've chosen there too. Does it need to be three books? I rather doubt it.
2) What am I getting? Does it have good art? Is it generally high-quality?
Like, the value of what you're getting matters. Good art, for me, will really significantly raise the price ceiling. If it's a physical product, the perceived quality and number of pages does really raise the price limit a lot potentially. Anything that's "digest format" absolutely lowers the limit a ton for me lol. As does anything like the demented "3 64-page hardcovers" approach of modern Spelljammer. You're giving me something I actively don't want. That has actual negative value.
3) Is it by someone - i.e. a person or company I know and like/respect?
This is a smaller factor but still matters - I will definitely pay more for, and feel better about paying more for a product from an author/company I like. Like say, Grant Howitt and Rowan, Rook and Deckard, I buy most things they make in PDF at least. Whereas WotC? Pfffft. Actively lowers how much I'm willing to pay - they're a massive corporation and they've managed to destroy all good will I had towards them over the last few years (I don't hate them or anything, but like, they get no more breaks than McDonalds' would, say), and they absolutely don't need my support.