So it's a biiiig rabbit hole, then.

Well, Factorio price policy says that they will never have a discount for their game. Full price only so you're committed.

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!

Yeah, exactly.

exactly why paradox introduced a subscription for Stellaris’ DLCs at 10€/month

I didn't even know there was such a thing. Sucks, though.