It depends if they replaced the whole regulator or just the cable , depending what happened (wth other people's lower quotes).
Both of mine have been done but under warranty. I don't think that cost is all that bad. The part is a generic price, and not esp cheap even if you're doing it yourself. Time allocated to put the car in the garage, disconnect the battery, door card, membrane and sealant removal, airbag, replace the part and then reverse. A new membrane alone if they replace it as part and parcel is over 30 with vat alone if you want it done properly.