Tough Weld currently has the Bessey DHCC-4 4″ Double Headed C-Clamp for $9.78.
The Double Headed C-Clamp is what the name suggests, a c-clamp with two heads sticking out in a “Y” at a slight angle (looks about 60 degrees, maybe?) from either side of where the head would normally be, much like a two-headed snake. The utility is that this gets around possible obstructions that would prevent a normal c-clamp from being able to grip securely. It also gives 3-point clamping, which is a lot more rigid and likely resists the twisting that you can get with an ordinary c-clamp.
The c-clamp is also available on Amazon for $10.72 w/ SS shipping.