This Instructable shows a quick and cheap setup to melt a few batches of aluminum for casting before the thin metal equipment starts to break down. Actually the 5-gallon bucket furnace will last quite a long time, over a dozen uses easily. This uses BBQ charcoal as the fuel and a hair dryer as the blower, it'll melt a small batch of aluminum in about 10 minutes. Most of the materials to build this can be found in dumpsters; the only cost here is the charcoal fuel, duct tape, and the $1 yard sale hair dryer. Recycle old lawnmower parts, computer/stereo parts, and beer and soda cans to make awesome new things with them.
For the furnace, two five gallon metal buckets (with lids) were used, a piece of 3-inch stove pipe, hair dryer, and of course, some duct tape.
For a crucible (the little bucket that holds the melted metal), a 16 oz propane bottle was used; the top was cut off and some bolts were added for grabbing the crucible with the tongs.
I made some basic tools with some scrap steel from an old bed box spring. You'll need tongs for the crucible, some kind of shepard's hook to tip the crucible when pouring, and a plain rod with a little bend at the tip for poking things and skimming out the dross (impurities in the aluminum).
Use of this equipment shown is dangerous because of very high temperature molten metal, fumes and smoke, etc. Use caution and be safe by wearing leather gloves, face protection, and other protective clothing. Do this outdoors and use it when it's a little windy so the smoke and fumes quickly dissipate, also use this during dry conditions because dripping molten metal on wet surfaces can cause little hot metal explosions (like water and hot oil in the kitchen). I'm not liable for any injuries you may occur using the equipment and techniques shown here.
Read, read, read lots of metal casting stuff before starting.
Casting Aluminum at submarineboat.com
BackyardMetalcasting.com ...Melting and casting metal yourself
Here's a silent movie of the foundry at work.