Not sure what the shuttle costs but we always just do an Uber/Lyft ride from SNA to Harbor. Right around $30 typically to give you a comparison to shuttle.
It's extremely easy to use RideShare at SNA. Just follow the signs and it's a short walk to the pickup place. I waited about 5 minutes for my Uber to arrive.
I thought of EVE before. I guess the discussion was more about what it would do that Uber or Lyft wouldn't (would be good for a solo traveler though). But if you're really talking about "the most economical":
Our Authorized Disney Vacation Planners are here to provide personalized, expert advice, answer every question, and uncover the best discounts.
Let Dreams Unlimited Travel take care of all the details, so you can sit back, relax, and enjoy a stress-free vacation.