I object to calling people chatting online artists.
However, ultimately nobody is going to pay them more than the value of their posts to the AI company which puts a severe cap on what that’s actually worth. People who post a great deal of online content might be worth compensating a few thousand dollars, but it would be hard for them to then turn that down.
I think the lower bounds of someone signing away rights to their whole art portfolio is more towards $1m than few thousands. Few k is just a month's salary that they can "make" themselves. Offers that small would be almost off-putting.