Modern, read electric, equipment is great when it comes to casting lead balls for shooting. What the electric lead melting furnace offers is the potential for greater consistency, as well as speed in casting.
HOWEVER, a person can cast nearly as quickly, and just as consistently, with a stove, a cast iron pot, and a ladle.
I know this because I started casting lead balls in 1971, at age 17, for a .45 caliber flintlock longrifle. A simple, iron, scissors mold; a pair of diagonal wire cutters for cutting the sprue off; a ladle made out of a commercial S.S. serving spoon bent into the shape of a ladle with a pour spout (pine handles sandwiched around the S.S. handle w/small bolts for insulation); a 3-qt "El Cheapo" aluminum saucepan for a lead pot, and an old bath towel to drop the hot lead balls onto out of the mold.
I used my mother's natural gas kitchen stove as a heat source. We lived in a row house, built in 1951, and the exhaust fan was a simple 6" diameter fan blade set in a round steel tube between the inner wall of the kitchen, and the outside brick wall of the row house. The stove butted right up against the inner wall of the kitchen, with the front left burner directly under the fan opening in the wall.
My lead source was two 25 pound bags of lead buckshot, approximately 0.457" diameter, that had been purchased for a replica 1860 Colt Army .44 caliber revolver.
After casting about 50 balls, I figured out how to regulate the temperature of the burner to create a nice shiny ball when cooled. No thermometer, the books of the time didn't even mention lead temperature, as I recall. Keep the pot at least half full, so the lead doesn't cool off too much while casting. Puddle a nice big sprue on top of the mold each time. Drop the cooled balls on the bath towel. When completely cool, cut off the sprues with the dikes as close to the ball as possible. Eventually, I made a second spoon for removing the dross after fluxing. Flux was paraffin wax.
Never weighed a ball. Never cut one in half to look for voids. Simply took on FAITH that what was printed in the Lyman Black Powder Handbook, Muzzleloader magazine, and Muzzle Blasts magazine was GOOD information.
And, it WAS.
Those "crudely" cast lead balls, shot out of a Douglas GAA .45 caliber barrel were capable of 50 cent piece-to-silver dollar sized 5-shot groups at 100 yards all day long.
So, don't think that the only way to make lots of balls, quickly is with an electric lead melting furnace.
You could get an old gas stove for next to nothing. Have it converted to use propane. That way you can work at waist height. A large, flat-bottomed, cast iron dutch oven will cost new about $75.00, and depending upon what size is purchased, could hold upwards of 100 pounds of lead. A thermometer, a casting ladle, and a skimming ladle. And ball molds. A good exhaust system, or fan to blow fumes away from your face. Or, a lead rated respirator.