Nebula is US$50 per year if you go straight to the website, but $30 per year if you click through any one of the creators' own referal URLs. No region-specific pricing as far as I know (but YouTube does have region-specific pricing, which is slightly cheaper in Australia than America using current currency exchange rates, which is why Nebula is more expensive here than in America, in YT-months).
The vast majority of Nebula content is available on YouTube, albeit with sponsors/ad reads removed, and sometimes a week or so early.
There's a fair amount of Nebula "Plus" content. Extra or supplementary material to videos that are otherwise available on YouTube, or an extra video in a series where most of the series is on YouTube but this episode is not.
There are also Nebula Originals, where Nebula themselves helped fund the project and the video is exclusive to Nebula. There are quite a few of these, but they're less common than the other categories.
The entire library is available to browse for free without an account if you go to their website and hit Explore so you can see for yourself. Look for the Nebula logo star for Originals, the + sign for Plus content, and the lightning bolt for Nebula First. You can also use the filters near the top to see only those, if you want. To give a rough sense of the relative abundance, my tablet displays up to 9 thumbnails per screen, and when sorting by most recent, the oldest I see without scrolling is 20 March for Originals, 30 April for Plus, just 9 May for First, and when unfiltered it only goes as far back as 19 hours ago, including 2 Nebula First videos.
some companies just convert dollar values to local currencies
This is what Dropout does I think. It displayed some weird numbers like $91.74, but didn't actually say anywhere that this was AUD until I read the fine print, so I almost started out comparing it to the US YT price. I assume the US price is a more round number.
Nebula just displays US prices and charges US prices regardless, I think. It's been a while since I actually looked at how they do it.