SeaWorld’s website is currently saying select nights from May 22nd - Sep 6th
https://seaworld.com/orlando/events/electric-ocean/
No additional cost. It’s included in your park ticket just like the night time entertainment at the other parks. There’s optional add ons such as reserved seating that you can buy (but I don’t think it’s worth buying having done it in the past. We had a better view sitting in the non reserved areas tbh) but you don’t have to pay anything extra to enjoy Electric Ocean. I highly recommend it because it’s some of my favourite night time stuff out of all of the local parks.