Some spend thousands on gear to make something that can only do half the job that your imaginations can. I needed a shoulder mount for work and was looking at spending $500 to $1000 to get one... Now that seems crazy when there are hundred dollar alternatives out there, but most of are poor quality to say the least. I'm going to show you how I simply took an $11 piece of metal, used half of it $5.50 and made a shoulder mount adapter for my existing rig. It may not be to your liking, but if you like what you see, hopefully it will spark some creativity on your end.
Read the hold instructable before you begin, some steps may come in different order for your purpose.
Made this at techshop.
Step 1: Steel
Note: Look at the next step, it will be easier to drill holes before bending, but...
Stop by your local hard ware store and pick up some steel. This piece was about 3.5" wide and 24" long. Grab a saw, cut it in half, bend it over your shoulder and now your 75% done. Yep. That's the first step (or second).
Obviously you should figure out what you will be mounting it to and how, so continue to the next step and maybe come back to this one if need be.
Step 2: What to Do
My existing support rods have threads inside. So I found a bolt and found out that a standard 1/4" bolt fit the job. 1/4" 20 (thread size) is pretty much a standard in the camera industry. Find a bolt that fits and take more concern to it's length. Too long could stick out too far. This one was 1" long.
I picked up a lock nut to secure it for good and then drilled two holes in me metal the desired distance apart.
Step 3: Putting it together
I used some sand paper on an angle grinder to get the shiny-scratched look, but recently decided to powdercoat it black for the final. Your choice. If you leave it "brushed steel" I still recommend a clear powder coat. Want to learn to powder coat, visit techshop, it's worth it. The padding I found in an old camera bag, but once again, comfort is up to you and it should be dead simple to find something you'll like.
And there ya have it. Quality and low cost. After making this I found out I don't like shooting with a shoulder mount anyways. (bad on the lower back), but at least I didn't spend all that money on something I wouldn't like. :)
Bob's your uncle.