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":
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