Hi,
I'm surprised no one else answered this yet. I've seen 1978ish Gucci Sevilles, I don't recall seeing a 1985.
Aside from the rare package the condition of the car is the #1 factor in value. Plus 1985 had the notorious 4.1 motor.
If you can post some more info on car, like condition, mileage, location, maybe some pictures, someone can give you a better idea of value. Also look on eBay or autotrader.com and see what similar condition 1985 Seville's are going for.