How about getting them laser cut first? Thin sheet can sometimes be a bit of a bear to mill, because its rolled pretty hard. A person might cut a prototype on the mill, but after that...well, its just not as much fun as it should be
Considering that a laser is non-contact cutting, and cuts as fast as you can draw a line with a pencil, a small lot order would not be that expensive. Sorry if I took all the fun out of your project
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)