Firstly there's the obvious...
-Straight, this is all process related, and you might have to run a good few hundred metres to get it, along with associated cooling times
-Surface finish, needs to be good to get the plating to stick
-Plating, extrusion grade aluminium is normally very soft, you'll need a hard coating to stop is gouging, probably not in the price per metre
There's a whole load else that can go wrong on these processes. I know it always looks like a lot for what it is, but the cost is there to cover the fact that it's not as easy as it appears!
Aidan