Step 1: Parts
For my purposes, it sufficed to have 1/2" steel pipes as the main structure. Make sure that you get galvanized pipes so that they don't rust from being outside!
Five 36" long 1/2" steel pipes with threaded ends
Four 9" long 1/2" steel pipes with threaded ends
Five 1/2" 90 degree threaded elbow joints
Three 1/2" threaded tee joints
7 bags of Quick-crete Cement
total ~ $50
gravel smoothing paddle (i'm sure it has a real name..)
a few spare bricks
In addition, I had played around with cement before, and it was a PAIN to mix by hand. For this project, I went ahead and rented an electric cement mixer. It came to about $40 for the whole day, and that was well worth the saved time and energy.