I didn’t know the origin of “well-heeled,” so I looked it up:
Originally American English, from a literal use in cockfighting: a well-heeled cock was provided with sharp spurs and could inflict maximum damage. From this developed the American frontier slang sense of being well-equipped, and thence the modern sense of being well supplied with money.
This probably also explains the use of the word “heeled” to mean armed (as famously heard in Tombstone when Wyatt is taking over the faro game.)