Cheapest stove I've ever used is a twig stove made from 2 coffee cans.
1) Cut a coffee can down to about 3.5 inches tall or so. (I used that size because it fits inside my cooking kit - you can use the whole can if you want but there are better designs for that.)
2) Snip the cut rim every inch or so and fold the edges down.
3) Use a can opener (the kind that punches a triangle) to punch 6 or 8 vents along the bottom and top edges. They have to line up with each other because....
4) Use 3 or 4 of those pairs of tabs to make your raised cooking surface by....
5) Drilling or punching holes in the top and bottom tabs and
6) Inserting 4 or 5 inch nails in them.
7) Cut the bottom off another coffee can by cutting it about 1/4 - 1/2" from the bottom

Give the same treatment to the raw edge, leaving a slight rim
9) Set that on top of the nails to make your cooking surface.
Without the top on, build a little fire in the can or transfer some coals over from your campfire.
You don't really need the can bottom for the cooking surface but it helps to keep your cookware from getting hella sooty.
Put your pot or pan on the top (or directly on the nails if you don't mind the soot) and cook away. Feed the fire twigs in the space between pan and the top of the can that is created by the nails.

Cheap. Kinda fun.
Pros should be fairly obvious. As long as you have stuff that's burn you can cook. I sometimes use homemade "fire starters" to just cook with. Toilet paper tubes stuffed with dryer lint, saturated with parafin and cut into discs.

Cons: Yeah, pretty fiddly. You have to constantly tend that little twig fire. Its also pretty sooty - best to cook with a lid on your pot/pan unless you like catching floating ash in your food. Pulls the nails out and put them inside top pack it down a bit smaller - but its ~really~ dirty so you need a bag to put the whole deal in.
I made mine with 6 air holes and 3 sets of nails. I'd do it with 8 and 4 the next time: more stable.