Yet another alternative is 1" by 3/4" by aluminum angle channel. Both Lowes and Home Depot sell it on the hardware isle. About $5 for a 6' piece as I remember.
Definitely go with the 1" x 3/4" aluminum angle channel. It works REALLY well.
It can be cut with a simple hack saw, even the cheapest ones (aluminum is VERY soft--you could even probably cut it with a good Ginsu knife!). You can drill in it with normal wood bits (well, steel bits, made for wood

) and you can use a countersink bit to make a nice dimple to level the screw heads off (use oval head screws)
A 36" piece is only $1.49 at Menards (if you have them, slightly higher at Home Depot and Lowes) They should have longer ones too. I used 36 as I was building a cabaret that only needed 18" top and bottom.
It's going to be more durable than plastic. You will need to prime and paint it however. Scuff it up with a 120-180 sandpaper/sanding block, use bare metal spray primer, then coat with whatever color you want, a couple coats and bake in the sun. Do the same thing (sand, prime, paint) the screw heads too.
Mine turned out very nice. If you want a little rounded look instead of the sharp edge, you can take a sanding block and sand it down a tiny bit, but you won't reach a high level of curve, just a small soft edge.