It is a bit unreasonable even for Volvo. The 940 alarm has an external
programming rig, the parts guy offered to put it on for nothing if I
bought the key fob, in the end I wasn't sure if the unit was faulty or
not so I fitted a new alarm for the price of 2 volvo keyfobs. Most of
the wiring was already there. I guess you went through the service
centre, these guys rely on people with lots of money spending it on cars
<5 years old. If you bring them a 6 year old car with an unusual fault
they say 'its the age of it sir, you'd be better of with a newer one'.
The parts guys are used to dealing with us bargin hunters. Even then
the key fobs are about GBP50, which is mad when you think about the
parts cost (about GBP2).
If you can get the unit out yourself, you might stand a chance and just
have to pay for the part. I've no idea how difficult it might be on the
S80.