I've only seen it in the 4 panel comic form

I couldn't tell you the original author, but it has the same decreasing-amount-of-money flow every time:

A young Jewish boy goes up to his father and asks for $20 to attend the school field trip the next day.

"$20?" says the father... "What do you need $10 for?"
"$5 is a lot of money."

I feel like I've seen Norm MacDonald tell his rendition of the joke, and I generally recommend Norm's telling of a joke over anyone else's.