Our mesolithic antecedents had a good building method that I started using for kayak racks in my back yard.
Using a "Metal Fence Post Driver" (a 3" steel tube with a weighted end and two handles used to drive metal fence posts.) I'd been using it on Home Depot 2x3s.
To hang my hammock, I thought to use a 10' 2x4.
It worked great. I think it could be done with Home Depot 2x3s, about $2 each, and the Fence Post Driver...one of your neighbors probably has one you can mooch. Cheapest kayak stand, well, after all those free trees.

I had to hack the 2x4 down to fit the pile drive tube. I also hoped to drive it deeper into the ground.
Today I tried it out. It worked well. My backyard is hardpan-desert dirt that when it dries out leaves salts --basically it's dirt aspiring to be concrete. I wasn't able to drive the posts even 24" One I think is about 18" the other 22". The angles in the design are 20 degrees, They worked out as 25 degrees and 15 degrees.
The ends are really flexible-- you'd hardly believe they're regular 2x4s. They wiggle a lot, but they don't do any work where it meets the ground. I think they enhance the hang.
The basic concept of driving a pile is that kinetic energy is critical, so yank the driver down hard. And drive the post until it won't go any farther.

Will up N down
Backyard Hang.pdf
PileDrivenPost.jpg
IMG_1928.jpg