Simply to say, the camera cage is used to protect your device and it can be an extension bracket for extra accessories. It also makes your shooting more stable and smooth and good for low angle shooting.
HDRiG offer the camera cage below $100.

The Basic Camera Cage is very practical and lightweight. With array of 1/4"-20 and 3/8"-16 mounting points on the cage rig for attaching accessories and universally compatible with most cameras less than 124mm in height.

It only cost $39.

This a universal cage with Double Rod Setup.

It is the basic full-frame cage that fits for a wide range of cameras under 131mm high. It equipped with a double 15mm rod setup, provides more mounting options on the rods. The array of 1/4"-20 and 3/8"-16 mounting points on the cage for attaching accessories. It has a NATO rail quick release baseplate to help achieve quick and easy lock & release.

It only cost $49.

This universal camera cage is the most popular cage in HDRiG. It comes with an cheese top handle and a left-side wooden hand grip.

The cage not only protects your camera but so provides numerous of mounting choices, features 1/4"-20 mounting accessory holes so you can mount accessories to your camera without stressing the body.
      Quite sturdy, no rattle noises. It can fit most of the cameras. Stable grip and easy to reassemble.
      It only cost $84.8.

This camera half cage can be used with Sony A6000 A6300 A6400 A6500 A6600 4K Cameras.

The special design of the cage gets the battery cover avoided from covering up by the cage and it has plenty of 1/4"-20 mounting points for attaching more accessories. It features a quick lock and release wooden top handle with NATO rail, which can effortlessly attach or detach with a hand-tight knob.

It only cost $96.9 (basic cage is $42).

This Standard Cage Kit is an adjustable half cage with a wooden top handle. You can adjust not only the height of the cage but also the top and base plate to fit any DSLR camera with height within 68mm ~ 130mm. With the Manfrotto baseplate, it can be mounting and removing quickly.
      It only cost $ 99.