Once a concept car has made the rounds at auto shows and other industry events, it's often locked away, never to be seen again. Worse still, some concept cars are destroyed after they've done their duty, as most manufacturers aren't too keen on the idea of their one-off creations becoming public property. Occasionally, however, there are concept cars that make their way onto the used market, and they present unique opportunities to own a piece of automotive history. Just take this 1999 Cadillac Eldorado Touring Coupe, for example. A Y2K Caddy Custom That's Oozing With SoCal Style 1999 Cadillac Eldorado Custom - 8Around the turn of the millennium, General Motors commissioned the Caddy you see before you — dubbed the EldoRODo — as a one-off custom to be displayed on the auto show circuit. As the car was intended to be a celebration of SoCal car culture (specifically lowriders and hot rods), GM tapped Huntington Beach-based California Street Rods to complete the build. When General Motors went bankrupt in the early 2000s, the EldoRODo was sold off along with other concepts and show cars.Though the powertrain and cabin remained untouched, the outside of the car was heavily modified to give it the slippery look it wears today. Beyond chopping the roof, raking the windshield, and shaving the trim and turn signals, California Street Rods also fitted the Eldorado with narrowed headlights, extended rear wheel skirts, and some plastic rear side windows. In keeping with the streamlined design, you won't find any side handles — the doors are opened via a set of remote poppers. 1999 Cadillac Eldorado Powertrain Specs CadillacElsewhere, the EldoRODo wears a set of custom-fabricated wheels, some rear air shocks, and a set of straight pipes that are nestled within the rear bumper. Like the McLaren Speedtail, it relies on a set of cameras rather than traditional side mirrors, with the optics displayed on the central rearview mirror. How It's Valued Compared To A Regular Eldorado Bring a TrailerIn the years since General Motors first sold the EldoRODo, the car has been to auction several times, and it's commanded less than you'd expect for a one-off concept. Though CarScoops reports that the Cadillac originally netted $60,000, it sold for less than $20,000 in each of its subsequent transactions. Classic.com records a private sale in 2009 of $15,000, while a 2016 Barrett-Jackson auction cleared some $17,600, and a 2023 Mecum auction saw it go for just $12,000. Previous EldoRODo Sale Results 2009: $15,000 2016: $17,600 2023: $12,000 Interestingly, those numbers put it just above the average sale price of a standard production 12th-generation Cadillac Eldorado. On Classic.com, 1999 models average $10,181, with the highest $33,000 sale going to a convertible conversion in 2022. Hagerty's Price Tool puts Eldorado valuations even lower — 'Excellent' examples will run you just under $13,000, while 'Concours' finds are priced at $17,700. At the time of writing, the EldoRODo had cleared over $19,000 on Bring a Trailer, so it seems that bidders are coming around to the quirky Cadillac coupe. Given that it was recently owned by Tyler Hoovie of Hoovies Garage, we can't help but assume that the extra publicity has helped drive up the price. We'll be watching this concept car to see where bidding ends.