Mine's insured for $14k as a low #2 condition car, but not sure if it could ever sell for that. 73-77 cars are kinda volatile valuewise, and the 350 car is way more common than the W30, if a total of 1420 cars can be called common. The black car is rarer than the white in either 350 or W30 guise.
Run the VIN thru the Hurst Olds Club (
www.hurstolds.com) and see if it was an Indy 500 Festival car. I'd pay a premium for one with that pedigree. H/OCA also has a price watch and can tell you a realistic value for it.
The 74 is a fairly easy one to restore since it shares almost everything with the Cutlass. Hood ornament, stripes and floorpans are repro'd. Worst thing to find will be the grilles and the seat upholstery material.
I'd check the front end close to make sure it hasn't been wrecked. A 1974 Hurst should have its parking lights in the lower bumper with blackout horizontal bar grilles. If it has vertical bar grilles and parklights between grille and headlights, it's had a nose job.