>If I declare a banana to cost $1,000,000 but you can get it for the low price of $1 with a loan of $999,999 today and that loan gets canceled, does that mean someone else has to pay me the remaining sum?

The contract would likely be ruled invalid for being unconscionable, because the fair market value of a banana is like 50 cents. However, if it was something like 10 cents upfront but $10 later that would likely be upheld.