When I cosplayed the boss (and used for female naked snake)I made my codec from scratch.
Like Sparrowhawk mentioned you need a throat mic, I can't remember how much a paid for mine but yeah the cheaper the better. Head to poundland/99p shop and pick up a cheap pair of earphones. Also while your there get some foam sheets, black electical tape or duct tape, silver paint (spray, acrylic or nail polish), black and white acrylic paint for detail and one of those crappy phone cases with a clip on the back (or just a redundant piece of plastic you may have lying round your house). Ok so making the codec is pretty bodge central but can look really effective.
Step 1: Make a small box out of foam.
Step 2: Make the front details out of foam (a square the same size as the box with a circle cut out and then a circle dial)
Step 3: Paint the whole thing Silver.
Step 4: Paint remaining details with acrylic paint.
Step 5: Hot glue clip you ripped off crappy phone case onto the back of the unit. (you will need to add a webbing strip horizontally onto your harness in order to attatch it or you could skip this step and just hold it on to the harness with duct tape? This is what I did because it was made in a rush :S)
Step 6: Put your harness on and place your codec onto the harness in the correct place. Now put on your throat mic. There should be a cable running out of it out the front. Guide this cable and make a hole in the top of the codec to put the wire through (this can be hot glued or taped for security.) Make sure you have enough slack to move your head without ripping it out but also not so much that it's dragging
Step 7: Cut one of the earpieces off the ear phones. Tape the cut to prevent weakening the cable. Put the earpiece into your left ear and the cable along the black of your neck and again push into the top of the box. (Hot glue/tape for security)
And ta-da you have your very own codec and all for under £10

You can do it another way where you make the codec out of clay and then make a silicon mold and cast it but this will make it more expensive and the method described can look really effective. If anything doesn't make sense feel free to pm or post

Hope that helps
