lol! My guess is they'd say "Oh yeah? In that case here's an invoice for..(endless list).." you don't want to risk an invoice in return from the parents!Although you might try giving them an invoice for your cat's little salad course. Not sure how that would go over with your folks.
My dad has a small deep freeze (saves a lot of money on food he says) but his apartment charges him an additional $15 a month to have it. I'm quite sure the yellow "Energy Star" tag on it when we picked it up at the store said it was only about $20 a year to operate. I wonder what his apartment would've done had they seen my various Nep setups years ago.