Just to add to this - if you can afford the space, and the opportunity presents itself - a second-hand 6x4 band saw would take an awful lot of effort out of the process. I picked one up for £100 (I think) and it has been one on my most-used purchases. Of course, being a sawdust eater you may already have a bandsaw - have a google and see if people recommend it for cutting metal (usually requires a half-speed gearing). A Jig-saw can work, but on thick ali a band saw just makes life better.