You are going to be hard pressed to find "cheap but decent" coils for our trucks. There is limited aftermarket support so what you see on these boards is what's available. Basically you can replace with stock nissan again, OME or AC coils. Replacing with stock nissan would restore your ride height to normal/eliminate the sag. I, however, do not know how much those cost. The wobbling you talk about it probably from your rear control arm bushings (do a search for this) and its a little bigger problem than the coils. Anyone else want to chime in?