I’ve used a Barska ACCU-Grip

I’ve used a Barska ACCU-Grip Camera Handle Pistol Grip for many years, both with a DSLR and with a small lightweight camcorder. It provides good stability and takes up virtually no room in a pack or travel bag. You can find it, as well as several similar grips, at B&H and Amazon, for about $15

The Vello CB-800 Universal Pistol Grip with Shutter Release looks promising too, although I haven’t tried it. Appears to be about the same price.