Sci-fi from '50s or '60s about aliens buy up all the private property in free world to make Earth a landing strip

[Donald]

I read this sci-fi novel from the library in '81 which seemed like an old and dated book at the time, probably circa 1950s or 60s, about a man and woman coming across a conspiracy by aliens to buy all the private property in the free world with an endless supply of counterfeit cash to turn Earth into a stopover for their spacecraft. The country ends up with countless homeless people because they sold their homes to the aliens. I remember it ending with the conspiracy being exposed by the heroes by somehow causing the cash money to revert to a giant ball of rubber-like substance, and talk of using an atomic bomb on it.