Try to get a picture or three of the damage and post it up. It might be mild enough that you can sand it down a bit, toss some por15 or similar to stop any more rust from spreading and weld a set of frame stiffeners on it. That would probably be the cheapest and easiest route if it's not too far gone. You have to remember that these Cherokees don't have a formal frame that you can easily cut and section in new pieces, it's a unibody.
1992 Cherokee Laredo - all stock, DD. Needs some minor rust repair, then on to the mods!
1996 Cherokee Classic - 3.5" lift / 31.0x10.5 Mastercraft Courser CTs / Warn XD9000i - Stripped for parts / junked :(
2004 Grand Cherokee Laredo - 4.7, bone stock - Wife's DD
NJ F-Body Owners Association