I'd think that if money were motive, then KC would not have sat on the missing story for a whole month until her mother forced her to admit she wasn't around.
In fact, her whole ZFG story sounded like a hasty excuse that she didn't want her mother to inspect too closely; it was not well fleshed out with corroborative details and the particulars tended to change with the clock. (And she changed her story of "give me another day, she's sleeping" to "the nanny took her" which makes me think she was nowhere near having a fake kidnapping/ransom thing ready for her parents.)
However, the minute the MIA story was fabricated that whole family jumped on the publicity bandwagon - whether initially to cover KC's abduction story or to profit is hard to say. But once they realized profit was a by-product, they went whole hog down that road and never stopped. The opportunistic way they handled it, angrily and defensively insisting that the fiction of Caylee being kidnapped and not dead months after the fact and with never a real SODDI in sight, made it look even more like they knew what had happened and were attempting to not only make lemonade from lemons, but were opening a lemonade stand and selling glasses to the public at highly inflated prices.
While the family behavior was transparent and despicable, I doubt KC thought too much about it ahead of time, or even she would have been far more organized about it and would have taken more pains to hide little Caylee's remains to milk it even longer.