Not difficult to rebuild if you have the tools. The worst of it is replacing the evaporator. That requires partly taking out the dash. It's also a known trouble spot. Buying the tools (AC vacuum, gauge-manifold, set of green O-rings, O-ring lube, PAG-100 oil, garter spring release snap tools, etc) plus the compressor (probably a good idea) and evaporator will be less than the cost of having it done, if you don't count your time. Then you have the tools when you are done.