There air bags in the back, and airstruts in the back. My system was very customized with chrome air tank, dual chrome air compressors. All custom made colored SS braided hoses instead of the plastic tubing, all brass manifold for the 8 selenoids, digital remote switchbox, computer control center, and digital gauge showing tank pressure and pressures to all 4 corners. It ran a a bit over $3000 with the wiring and labor. They dont make a GXP kit back then, and the front airstruts had to be custom fabbed.
You can bag for under $2000 for an entry level system, here'* the cheapest place I know.
Their Bonneville kit cost'* $1795 and real basic.