I am a dedicated DIY'r who can't say "no" to a new problem and I also am not cheap, just stubborn. So here is what I would do:
1) Research air-conditioner function and patiently trouble-shoot as best you can
2) check the many online salvage places for used units:"http://colawrvsalvage.com/" or "http://azrvinc.com/" etc. for replacement of the rear unit if necessary. Pick their brains for alternatives. The A/C's are all basic hookups with similar installation as far as I can see.
3) recharge/repair of the front may be possible. Does the front unit have a recharge fitting? If not (most don't) find someone who can SILVER solder one in, pull a vacuum and recharge the unit. Or learn how to do it yourself. If you are like me, there is a certain satisfaction KNOWING I can screw something up and IT WON'T COST ME AN ARM and A LEG........LOL
Good luck. I apologize for not sending you some sanity. I sometimes run short of it myself in these situations.