To MIG weld aluminum, you will need:
- pure argon as the shielding gas. Price is usually close to the price for C25 (which is 75% argon and 25% CO2). If you have to actually buy another cylinder, then that raises your cost compared to just 'filling' a cylinder.
- the aluminum welding 'kit' for your machine. That's usually ~$100 or so, and typically for the small Lincoln MIG machines includes a plastic gun liner (the existing coiled steel liner will chew up the softer aluminum filler wire and clog up fast, as well as smear oil onto the aluminum wire), some U-groove drive roller(s), some appropriately sized contact tips (aluminum expands much more than steel, and thus the 'normal' steel-sized contact tips will cause the aluminum wire to jam in the contact tip once it heats up as you are welding), and usually a 1 pound spool of 4043 aluminum welding wire.
But the 140C does NOT have an aluminum 'kit' available. It can use the Lincoln SG100 spool gun, plug-n-play, to weld aluminum.
tech note: 4043 and 5356 wire are NOT interchangeable. They are different alloys, and use slightly different welding parameters and not all 'small' welding machines (even name brand ones like Lincoln or Miller) can even run 5356 wire (they can't produce the correct volt-amp-WFS relationship).
5356 wire is a little bit stiffer than 4043 wire for the same diameter, but even so, trying to push 10+ feet a 0.030 aluminum wire through the gun cable is probably going to be rather frustrating. Small diameter aluminum wire through a steel gun liner? Even worse.
Either hire it out to a welder who has the proper 'tools' AND experience to weld that up, or you can spend at least $500 (about $250 for the spool gun and another $250 for an 80 ft3 cylinder of pure argon) and a bunch of time to practice welding aluminum. IMNSHO