Welcome to the forum. Monte looks to be in pretty good condition. Replacing the rear frame sections on these cars isn't a bad job really. The frames are the same on 78-87 Cutlass, Regal, Monte, Grand Prix, & 78-83 Malibu. Even the 4 doors have the same frame, only the wagons and el camino are different. This leaves a wide variety of cars to look for that are being parted out that you could get the rear frame section from. I found a guy with a rust free frame from a 78 Malibu and he cut the rear sections off for me for $30! All you need is a sawz-all, grider, and a welder. You could always pick up a cheap welder and practice on things until you're ready to tackle the frame. I replaced both of my rear frame rails for about $65, that's including the rails, undercoating, a new wheel for the grinder, and a sawz-all from harbor freight as well as blades for it.