[As a warning, as cool as the rivets and steel look, it was a lot of work, the ducting isn't meant to be put together like this and thus everything is really tight and the large flat areas want to buckle. Also, cutting an oval shaped hole in sheet metal is a lot harder than it would seem.]
Cost breakdown:
-Radio ~ $60
-Speakers ~ $30
-Power supply ~ $20
-Anderson Connectors ~ $3.50 ea. (not necessary but add a lot of versatility to the power supply.)
-Housing ~ $30
-Total ~ $150
Note: This is not a cheap build from scratch, hopefully you happen to have a radio or speakers gathering dust and this gets them back in use.
Below is a close up of the power supply and cords. As you might have noticed the power supply on this radio is not in the housing. The only reason being that I was using it at the time to power a DC mini-fridge when it wasn't supplying the radio. That is also why this build used the Anderson Connectors as I needed to be able to change to a 12v power point receptacle for the fridge. An added benefit is that AndyMark sells a nifty adapter to convert Anderson connectors to alligator clips, which would allow you to run the radio off a car battery. (Link)
