The best way to evaluate prices is looking at what prices people paid on recent sales. I'm very found of the "completed listings" check box on eBay as it tells you what people really paid. That kind falls apart when you search for "Caravelle", which is not a common listing. That being said, look at the prices other similar cars bring: Diplomat, Gran Fury, 5th Avenue, Crown Victoria, Old Cutlass, Buick Century, Ford LTD, etc. If we are being honest, these are everyday cars that don't get the juices flowing in the collector's market. Exceptions are made for extremely well preserved, low-mileage survivors. If you post extensive pictures here with mileage, I'm sure the community here will offer some guesses at what it might bring at sale.
$.02
Adam