It sounds like you are looking at a pretty good car. A lumpy idle could be dirty injectors or more likely it just feels lumpy because of bad engine mounts. Neither is hard or expensive to fix. The slowness off the line could be a simple clogged air line to the ALDA. If you aren't seeing a lot of smoke or other signs that would suggest a bad turbo or worn engine then that too should be an easy fix. The windows are not vacuum powered so that may be a bit more complicated. The motors are pretty robust but the regulators and fuses do often cause problems. the good news is that parts are pretty available in junk yards so I doubt you have much of an issue there. The hard shifting is also likely a vacuum issue but that's a bit harder to know without some experimentation. If the shifts are solid and there doesn't appear to be any slipping the chances are good the fix will be simple. The AC is a different story. The compressors are prone to failure and a proper repair (one that will last) requires a new compressor, complete flush and new receiver/drier at a minimum. If you want AC it will likely cost you. Now about the price, others here may disagree but I think the price is on the high side. If the AC where properly repaired I might look at it differently but cars with needs are seldom an easy sale except to people like us who know the cars and can do the work themselves. That said, a 123 wagon with no rust and relatively low miles is a car you could use and enjoy for another ten years. You need to decide how much that $2,500 is worth to you. At a fair price and with a through look over, my sense is that this car may be worth taking a chance on

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold