Premades tend to range 40-100, and "originals" using stock imagery and some photoshop work $60-~$250 I've seen depending on how much work is done. From what I hear, a ton of people get good deals from creators/artists for various reasons (ongoing work, friendship, whatever).
Original illustrations on the other hand jack everything up considerably. I mostly read and write fantasy, and for the non-symbolic stuff (like the art used on ASOIAF or First Law) we're talking $250-600 on average and yes easily up to $1000 or more for covers that can and do easily double as elaborate hangable works of art. I've seen some pretty darn good artists on DeviantArt charge far less, but they're definitely undercharging. Most of them are in countries where the US and UK currencies goes further and many of them don't understand the idea of a commercial license; in fact, a ton of them just give you full rights to whatever they create for you. Not sure what the legality of all that is between countries, but the point is it's a tangle already.
I guess it really ultimately depends on the genre... I freaking despise the standard romance cover with all my soul. I struggle to understand how anyone likes them, especially since they're so generic. But it's what romance expects, so it's what everyone does. Meanwhile, fantasy has a very strong cover aesthetic; your covers need to basically be pieces of art. If they aren't, many people won't even look at your blurb. I find myself that way too more often than not.
I mean, just look at this:
https://bookriot.com/2019/06/26/2019-fantasy-book-covers/In my very humble opinion, I think a lot of indie fantasy authors lose right from the start because of their covers. Granted, I'm only just readying to launch my very first novel soon, so take my words with a grain of salt. This comes from a few years of researching the indie life, purchasing artwork for other projects and looking for a cover artist for my novel, talking to some of the more successful indie fantasy authors, and my general opinion as a voracious reader of hard fantasy.