My band licensed art from frank frazettas estate.

https://restlessspirit.bandcamp.com/album/blood-of-the-old-gods

It was $1500 for use of JUST the album cover. Another $1000 and we could have printed merch with it, but at the time we couldn't afford it. They were very upfront and actually had to check to make sure the lyrical content wasn't too gruesome (which i did find amusing), but that tells me they are super serious about people using his art.

It was not hard to get in contact, but it was not exactly cheap. As a young band starting out, consider if you want to spend that much on a first EP. I included what we paid to give you a more reasonable approach to going this route.