Sportsmansguide (.com) has had a propane single burner stove (under stove) that has 3 rings in the burner and a control for each ring. Were $29.95 plus shipping (cast iron, not cheap)... Northerntool (.com) also lists them but $39.95. (Or you can get the 2 burner set up with 2 burners like this.) POINT: You have to have enough heat and concentrate it to get the lead to melt and stay at the right temperature. Camp stoves are lame and will take forever. Plumbers have a melting pot for this, but they are not cheap and you said money was a consideration. (There was an ad in shotgunnews(.com) for plumbers furnaces and lead...) House stoves and kitchen ranges are better, but still not up to this 3 ring level. The turkey fryer (at least the neighbor's I got a close look at) are for temps in the 325 F range. Couple of gallons of oil. No doubt, better than some 7,000 BTU camp stove but will spread the heat out.
You are going to burn some fuel. Propane? Nat. Gas? Oil? Wood? This takes some BTUs. It ain't free these days.
AND, to save/preserve the heat, find yourself a big piece of pipe, concrete or clay, that will fit around your stove/pot. You need to put it up a bit on bricks to let air into the base of the fire, but it will concentrate the heat some and save $$$... Should. If weight is a problem, you could use half of a burned out water heater... here electric is better, thicker insulation... to hold heat... And find a swim suit... You are going to do some sweating... luck