Retaining Wall advice needed, Cheap, Ugly and Easy!

(And so is the builder! ) I won't see this wall from my house, it will be propping up the backyard and back fence, which slopes from front to back (and side to side). It then faces a gov't school but is essentially out of sight behind buildings. I don't need advice on seeing the council or engineers either, that's all under control, but thanks anyway! I have an extremely limited budget, but can collect free/cheap materials to repurpose. Lets call the wall 1500 x .900 high, and aiming for as close to vertical as possible. I am after some input for cheap, unusual options to construct from, I have plenty of time on my hands lately! (The fence will be typical post/rail/paling) I do have the 1.6M galvanized sheeting from the original fence, and am wondering if this could easily be utilized as the wall, like these... http://www.cajunmarineconstruction.com/ ... Walls.html but then I also got looking at gabion stone baskets and wondered if i could come up with a cheaper alternative for this purpose, I have plenty of rock and rubble from pulling up garden paths, which lead me to wondering about using 44 gallon drums along the boundary, filled with rocks, bricks and concrete, topped off with gravel, and topsoil, scalloped top on the property side to sit well below ground level (usual ag-pipe/drainage behind of course) I could protrude onto the school a little, running the drums centre-line along the boundary, with posts for fence also mounted in these? Obviously these drums are taller than I need, but I could easily dig the trench to hold them or cut them down accordingly, how long do these drums take to rust through anyway?
What other ideas do people have for a cheap, effective wall material where aesthetics aren't at all important?