How high, wide, long are you looking for?
Does it have to fit a given tent?
I found a French mil-surp item that's only 6" off the floor and, so, fits my tent where higher models would not (due to angle of sides). It uses four steel legs that snap into the steel side rails and is quite comfortable.
I bought a tubular aluminum jobbie with three legs that stood 8" off the floor. Mistake. Although rated for fifty pounds over my weight, the side rails started to bend.
The Coleman folding bed sold at Walmart is comfortable, but it has a design defect and is good for maybe ten weekends. This is the experience of several. The cloth sheet that supports you has a steel cable in a tube sewn around it's perimeter. Springs attach the cloth to the frame by attaching to the cable, but the area between the folding halfs is too long, increasing stress. With use, the steel cable cuts though the cloth in the area between the folding halves. As more and more of the cutting takes place, the cloth sheet sags more and more. A flexible steel tube should protect the cloth against this failure. I see such materials but can't find a source.
I have seen what appear to be the identical cot selling for $x.xx, for twice $x.xx, and for 2.5 times $x.xx, so look around before buying.