It's a stable like ocha and such. Somewhere along the way, "okane" became the entire word, sort of how you always say "ocha" and "gohan."
An interesting thing is the "go" in "gohan" and the "o" in "okane" are the same kanji. It's just that the "o" indicates that the rest of the word is of native Japenese origin, while the "go" indicates that the rest is of Sino-Japanese origin.
The exception is "ocha," which comes from the chinese "cha1," but the word has become so much a part of the Japanese language, that subconsciously it is treated as a native Japanese word. Or so linguists would tell you
And I would say お金を持っている。 And the honorific prefix kanji is 御.