I've seen new fuel distributors selling up to $1,700., but hopefully that's not the issue. If the owner could have remedied the problem with only plugs and wires, I imagine that he would have done that already. Vacuum leaks also can cause rough idle - not expensive. Sounds nice for $2K. I bought mine with a rough idle - turned out to be fuel distributor but my mechanic found me a rebuilt one for about a grand - was already doing some top end work so labor wasn't anything additional - it's been fine ever since. My humble opinion - 126 is the best Mercedes ever made. If you like the car and it seems to have been well cared for (there aren't hot rods - they don't get beat up much), you should get it.

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1991 560SEL (254K miles)
1980 Lincoln Mark VI - Givenchy
1979 Lincoln Mark V Collector's Series
1979 Lincoln Town Car Collector's Series
1979 Ford "Effie" Pickup (in gradual transformation to a show/street truck)
1969 Lincoln Mark III (waiting for "Overhaulin" to call)
1989 Lincoln Towncar
2001 Lexus GS300 (spousal unit's daily driver)