Part probably isn't that dear, well more than a US made version, but after Miele USA factors in shipping from the EU and so forth would be up there. Labour would be a large expense,however if one was able to do the job oneself, not that big of a deal. I mean to pick up a Miele W&D set for under 100 USD. My only concern would be what else is going or likely to go if the timer is having problems.
Timer could also have been damaged by a child or someone else playing around or perhaps a substance was dripped or spilled down the front of the machine.
With proper care, old war-horse Miele washers such as these do tend to last quite along time. Very simple washers compared to the Navatronics, much like old mechanical automatic dishwashers and washing machines. Again much would depend on proper use and maintanence. No routine over-loading, proper detergents, letting the machine air out between uses.
Miele USA must have lots of these machines still out there, since last time I checked (several months ago), most of the parts are still available.
Personally, unless one lived close by and was able to purchase the set for under $100, wouldn't really bother. Seller's attitude bothers me, and would want to kick the tires at pick-up to see if he's not trying to pull a fast one.
L.