Stephen, I think the reason Columbo was scrambling for change to pay for his gas was because Mrs. Columbo keeps the checkbook, and pays all the bills, and leaves Columbo with a small allowance. Columbo and Mrs. Columbo probably had a huge savings account that they were gonna use for retirement, and the were very disciplined to stick with their budget.

Just my imagined opinion.

By the way, I really believe in the beginning of this episode we find that Brenner owes Geronimo a few hundred thousand dollars, (the "banna land" scheme) and that's the main reason he kills him.