I am a UK based Illustrator.
I don’t usually accept “work for hire" conditions unless budget accounts for copyright ownership. All other commissions are under licencing terms and conditions.
As a foot note: I have encountered or seen many propositions that are simply unreasonable, If you are in need of something realistic on the time it takes and the minimum budget to produce the piece of work. Being an artist is a job like every other, we also have bills to pay and food to buy.