Flatten Backyard

I am trying to figure out the best route to flatten my backyard to create some space for my son to have an area to play. I’m mainly thinking of 1 of 2 routes and I think both would require a retaining wall. First is dropping down a few feet after the deck. Send is building up the area past the arborvitaes and pine closest to where I’m taking the pictures. I’m taking the pictures from the end of my backyard. There’s actually a road that goes behind my house and that’s what I’m standing on.

How much am I looking at to make this happen? I live in Atlanta if that helps.

Let me know if I can add detail to help with your analysis. Thanks for your help!