To answer the OP, I do have experience with ballot measure petition drives, I worked for a company that did them purely on the local level for three years in college.

At the low end, it will cost about $1.5 million to get something on the California state ballot unless you have a huge source of volunteer labor that is willing to be trained in proper signature gathering.

The first steps are to come up with language that the state Legislative Office will recommend, and then poll it to see if you can try to qualify it immediately versus waiting for an election that will have voters more favorable to you. Off year v presidential year, primary election v general.