If you're looking for cheap speed with an exoskeleton, you've found it.
To be fair, calling the Exomotive Exocet an answer to the Ariel Atom isn't really correct. The cars are both minimalist track day machines, but the Atom is so much more expensive that it's fairly absurd to compare them. The Exocet is actually built out of a 1990-2005 Mazda Miata donor car, with an exoskeleton that is essentially just riveted on. This "base" model can be built for just a few thousand dollars.
You do have the option to upgrade though, with a crate GM LS3 V8 (the one used in the C6 Corvette) and drivetrain components out of a Cadillac CTS-V. If you don't believe it fits, just watch the video.