Honestly, you make some phenomenal stuff. I make merchandise and I would love to buy the rights to reproduce some of your art. Message me for more info on that if you're interested.
I'd say the best way to gauge how much you should be paid on a commission basis would be on the time you spent on the piece, but I'd say your black and white piece alone should be at least 10 USD to start.
I make bottle openers and pins for charity.
I am looking to hire artists and pay them in USD. Please contact me for more details.