What would a 1988 Olds 98 Regency Brougham be worth?

According to NADA Classic car guide, anywhere from $1,200 to $4,100, for base options. You can try their site yourself, and input options for a more refined answer: Nadaguides.com/Classic-Cars/Manufacturers . You can also try Hagerty and Hemmings, although those tend towards older classics. Not many people consider an '88 Olds a classic car, but you might still find a fan out there. Get it detailed and good pics and start shopping it around. If you can't establish a good price for it, put it up for auction and let the bidding begin.