What kind of work will you want to do on a 3/8" plate that you will have to worry about hardening?I routinely cut this and thicker material with torch, and have no problems with drilling, grinding, or bending the material afterwords. Possibly an easier, and cheaper way, would be to buy a cheap angle grinder from harbor frieght or somewhere. You can usually get one for under $20. Then buy some 4 1/2" cutting discs. Here is the real trick...mark your cut line, then clamp the steel to a work table. Hold the body of the grinder with your left hand, and hold the handle with your right hand. Make sure that the handle is on the left side of the grinder. Do not look directly over the cutting disc, but sight it in from either side of the line. This works extremely well, and is cheap to boot.
Stop talking about it and do it already!!!!!
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)