Any Sony A7s owner knows there are a few things this camera needs to get the best possible quality out of it. If you want 4K footage, you simply can't record to internal media, so you'll be adapting a recorder like the Atomos Shogun. The battery life is also terrible, so a decent external power option might be the IndiProtools Power Pods (found here).
With these accessories, you'll need a solid way to mount it to the Sony A7s. There's a number of rigs i've shown in the past, and this is just another great option to consider for your A7s. The CAME-TV Sony A7s Cage is available in a variety of bundles if you need extra items such as a Mattebox, Shoulder Pad, Handles, etc.
There are plenty of options for rails on the market, and I advise you to shop around, but for a pair of 8" 15mm rails with both Male and Female threads these prices are pretty darn good. Check it out at PhotographyandCinema.com (click here).
P&C 15mm Extension Rails with Male / Female Threads
Most DSLR Rigs use handle grips very similar to bike handle grips. In fact if you threw a bit of cash down, you can get Bike grips better than rig handles. Now how do you go about making your own custom set? Well first you need to get them down to fit the 15mm standard, so the video above by Vimeo member Jarrod is one way to accomplish this with a nice pro look. This technique requires a pair of 15mm rods and a pair of 90 degree clamps, so by no means dirt cheap, but you can end up with something worth much more than what's found in current retail. One way of saving a few bucks is to locate a single rod and cut it in half. [Thanks Jarrod]
You can find a variety of inexpensive 15mm Rig Rods and Clamps new and used at the auction site (click here).