the DLC are pricey, but they're also proper, old school expansions adding lots of content that actually enhances the game.
it's perfectly playable without the DLC, and there's a LOT of DLC-sized mods on the workshop!
kind of a fundamental problem with modern DLC: they generally don't get cheaper over time (remember when that was an actual thing? not just sales, but actually lower prices for older games?).
if you keep up with the releases it's super okay at about 20/25€ once a year, maybe twice, bur if you're late to the party it's a whole lot of cash all at once!
exactly why paradox introduced a subscription for Stellaris' DLCs at 10€/month... honestly kinda worth it, if you know you're just gonna play for a while and then move on...still wish stuff would just get cheaper at some point again...
It is also DRM free on Steam. You can copy the rimworld folder to a PC that's never had Steam on it and play it as an example.
You can also do that to sort of save a snapshot in time of Rimworld when they are releasing a new version that will likely break mods for a long time/sometimes forever.