I got a couple 4" grinders...I keep one loaded with a cut-off disc, and the other with a grinder disc. I also use flapper discs to do final clean-up. Maybe $100 for all my grinder stuff. Harbor freight grinders are absolutely useless, and I've melted several in half. I try to stick with a brand name unit (DeWalt, Bosch, Milwaukee, etc.)...and they seem to last longer. Cost for a good one is $40 or more...compared to the junk stuff at $15.
I use a Hobart 210MVP MIG wire-feed welder...and its a been a great one (around $900 online). The MVP stands for "multi-voltage-plug" which is a nice feature, even though I always use 220V. I put a gas kit on it and use standard solid core wire, instead of the flux-core it came with. I've tried flux-core on numerous welders...and all I ever get is a nasty mess! Pay attention to duty-cycle when shopping for a welder....that's what you're paying for.
My Plasma Cutter is a Thermal Dynamics-Cutmaster 42. ($1100 online). Its a good piece but, occasionally it acts up. I believe this is my fault, and has much to do with tip selection and my cutting technique. This is also a 220V machine, and it likes 80psi of air. This is the smallest one they make that doesn't have a built-in compressor. It will cut 1/2" plate...but not real pretty. It will cut 1/4" and 3/16" plate very nicely and that's the bulk of what I cut for bumpers, skids, and such. Tips and electrodes are expensive...and after a year or so of owning it, I finally bought a stand-off head for the gun. This seems to make the tips last much longer, and also makes a better cut. Plasma cutting is the only way to cut steel. True...that's all it does. But it does it so well! And yes...I installed a Miller filter/dryer ($75) on the incoming air line, just like someone recommended.
I have a buddy that I borrow an Oxy/Acetylene rig from. Its a craigslist special...two bottles on a cart for $75. It works for heating stuff up, and making nasty junkyard cuts. Its small and does the job. I don't know much about it.
This equipment is very compact and I used them to do my SAS and SOA with no problems at all. I still use them for building custom, one-off parts here at my home shop. However, all of the THORparts stuff is manufactured elsewhere, and they are done on computerized laser-beds, formed, and welded by guys that do that for a living. I'm getting ready to re-tube a high-pinion Dana 44 pumpkin, and I might run that up to the pros and have them do the welding for me. Like Scarsman says...certain jobs require more equipment and experience than I have.
