Indeed, artists provide a very valuable service. It's a shame the AI industry feels they're replaceable when they're obviously not.
Their price is based on supply and demand just like everything. If AI decreases demand or raises supply then their price will go down.
Basic economic theory states that only holds if the goods / services being provided are equivalent in the eyes of consumers. It seems self evident here that consumers do not consider them equivalent.
You said that the AI industry feels they're replaceable. I'm not saying that AI does equivalent work, I'm saying that AI companies don't choose the prices for art, they just play in the market.
But...they really don't? Everyone is replaceable, there's nothing special about artists.