Your prices are not entitled to be affordable to everyone, your prices are what people need to cough up to afford you. Somewhere along the way the prices for mass-produced posters became conflated for original fully-rendered art by request, and they’re not the same thing. One reflects the cost of printing pre-existing art on paper, the other reflects the cost of skill and labor.
Don’t compete with print prices when you’re a single person cranking out art. You’re a human being, not a printer. Don’t price yourself like you’re a machine and don’t let people treat you like you’re a ctrl+p shortcut.