1968 Ford Mustang GT: $3,000The 1968 Ford Mustang GT was relatively inexpensive during its original run. At a price of around $2,800 to $3,000, depending on whether buyers went for the hardtop or the convertible, inflation wouldn't put this ride's cost at much higher than $25,000 today. Despite this relatively modest pricing, the 1968 Mustang GT also had its own extensive marketing campaign, with one particular facet that sent it skyrocketing in value.One specific variant of the Mustang GT was used in the classic film "Bullitt" as the titular protagonist's car. The film was likely its most notable appearance, with the car featured in an intense high-speed chase. This specific model eventually found its way into an auction in 2020, selling for a whopping $3.74 million. There were extra alterations done to the car to justify its price outside of its fame, with its 390 cubic inch V8 engine being fitted with modified cylinder heads and an electric ignition system.As a result of its auction price, this vehicle is among the most expensive classic muscle cars of today. While it might not take the number one spot in that regard, and while it certainly wasn't able to take that title in 1968, the Mustang GT might have the most impressive increase in value compared to any similar cars.1970 Pontiac GTO: $3,500The Pontiac GTO featured numerous customization options in 1970, including a specially named Judge package. While some of these options could increase the price of a GTO by hundreds of dollars, the base price for a convertible was around $3,500. In terms of both modern and original pricing, this puts it at around the same level as a 1970 Chevelle SS. In fact, this similarity also applies to its eventual highest auction price.One particular 1970 Judge was sold at auction for around $1.1 million. Unlike many other muscle cars that ended up being worth over a million dollars, this wasn't due to any special history or previous owners. The reason the Judge sold for so much was due to its specs, as it featured an automatic transmission and a Ram Air IV V8 engine that could produce an impressive 370 horsepower. Though over 40,000 GTO models were manufactured in 1970, only six other Judge muscle cars with similar features were built that year. The 1970 Judge GTO is proof that rarity can affect the value of expensive products just as much as popularity can.1967 Shelby GT500: $4,200The 1967 Shelby GT500 is a notable muscle car that built on improvements made to previous models. Its base price of around $4,200 would be adjusted for inflation at nearly $40,000 today. One particular variant of the GT500, the Super Snake, featured the same 427 cubic inch engine that won at Le Mans in a GT40 Mk II. This version of the car actually managed to reach a price of $8,000 upon its reveal, which would have made it one of the most expensive muscle cars of its time. Unfortunately, a lack of consumer enthusiasm for this variant — not to mention its high price — meant it never found an audience, and only two are known to have been produced.That wasn't the end of the Super Snake's story, however. The original prototype of this GT500 variant was eventually found and sold for $2.2 million at auction in 2019. It's still far from the most expensive classic muscle car, but it's an impressive comeback for a variant that never made it to mass production.1967 Chevrolet Corvette: $4,388The 1967 Chevrolet Corvette boasted numerous customization features that led to various different prices. Yet its base price ranged from $4,240 to $4,388. With a couple more years of inflation, that could easily put it at the $40,000 mark today, even when ignoring its pricey additions like unique seating and special engines. In fact, those additions eventually allowed one version of the Corvette to become one of the most expensive classic muscle cars ever sold at an auction.The priciest variant of the 1967 Corvette featured an L88 engine. At 427 cubic inches and capable of producing 430 horsepower, it easily rivaled the performance of other top-of-the-line engines at the time. Thanks to this, an L88 coupe on auction reached a price of $3.85 million. This is higher than most classic muscle cars could ever hope to reach — even those with famous owners and iconic histories. Still, the 1967 Corvette falls short of at least one other muscle car when it comes to both base price and modern auction cost.