I'm sure I'll get flamed for this, but I use a Harbor Freight 90-amp flux-core welder with .035" wire (meaning the wire lets off gas as it burns, shielding the weld, instead of gas coming from a bottle, like a Mig welder. Gas coming from a bottle shields the weld better, meaning less splatter, but I believe flux-core can get more penetration if comparing the same amps. Shielding is required because hot metal reacts with the air). I've plated the chassis using a combination of 1/4", 1/8", and 3/16" c-channel and angle with this welder, chopped and plated the stock crossmember with 1/4" plate, welded on an LCA mini-skid, and a few other odds and ends with it so far. You get what you pay for, but this gets the job done for cheap with 1/8" and 3/16", 1/4" is doable but barely. The MillerMatic 175 is what I want eventually, but I've had this for a year so far, and it's worked well. I bought it for $120 and I've already had two offers to buy it for about $80 when I eventually upgrade.
Edit:
By the way, most cages are .120 wall (1/8").