I’ve heard license for UE3 were very expensive, after a bit of googling it seems like a full licence for UE3 without royalties was about $750,000 +$100,000 per platform, and may have costed extra per seat. It probably varied per agreement. I’d imagine UE4 is in the same ballpark, but they might be willing to be more flexible for smaller devs. Licensing agreements sometimes cover support, if you are shipping a $200,000,000+ AAA game, you’ll want any engine bugs delaying development to be fixed ASAP.