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Just did some poking around and found out it would take 155,216 signatures in 90 days to put a constitutional amendment on the ballot in Oklahoma.
Around 35% of signatures will be thrown out due to things like wrong county, voter name not exactly as registered, signature not exactly the same as what the voter registered with, "voter" not even registered, etc.
You're looking at $4-6/signature between professional collectors and campaigning.
As for the state statute option, you don't want to go that route. The legislature is free to over turn a statute at any time. A Constitutional amendment requires the People to vote to reverse it.