Check out http://ecomodder.com/forum/open-revolt-open-source-dc-motor-controller.html
if you want to read about the whole story!
Experience in soldering is important. If you want to really keep costs down, a mill is helpful, but that work can be outsourced to a local metal shop.
Step 1: Get/Make a power board and control board.
You could print the picture from this link and somehow transfer it onto a piece of heavy blank PCB, and etch it with a dremel if you have a ver y steady hand. The dimensions are 8"x6". This link also has the G-code that you can use to etch with a CNC mill or you could give the G-code to a machine shop.
Picture 2 and 3 below is an example of an early power board I made with a Dremel.
You can get a control board from me or you can make the control board in your favorite PCB layout software using the schematic here::
And here are some pictures of the PCB layers:
A predone control board is Picture 1.
Pictures 7 and 8 are the power board top and bottom. The 8 solder spots are just where vias were added.
Once you have the 2 boards, you can go to step 2.