I'd make that out of steel. It's weight is insignificant, and lower profile is more important than weight in this application. Steel will hold up to occasional hits on rocks and such, aluminum will crack and possibly fail dangerously when you use it.
Laser cut would be cheaper and better than water jet, you'll need a moderately high-power laser for that thickness steel. Laser doesn't do well with aluminum, if you stick with that. It could be milled reasonably cheaply from bar stock as well. Either way, it'll require two setups to drill the holes in two directions. If you make a quantity, a CNC mill will be cheaper than manual milling. Sandblast and paint or powdercoat can be done anywhere. Most powdercoaters run black regularly, can run a bunch of these for not much money.
If you wait 'till Spring I plan to buy a 100, then the 100 parts will start flowing!