Per his responses on Instagram $13,700. That may be the price on this build. Maybe the start a little cheaper if you chose different options...
I personally could care less on what anyone "calls" it when a quad kit is installed. All I know is that this type of setup will just kill any Slingshot in the typical stock 3 wheel configuration. This type of setup is not for someone that worries about classifications. To appreciate this, you really need to understand the performance and how it relates to other very fast and expensive vehicles. It is a legitimate go cart with 4 wheels that you can drive legally on the street and will likely embarrass Arial Atoms, KTM X-Bows, and other super cars in performance metrics.
I have one of the fastest, if not the fastest, track Slingshots in the country. I am quite literally out of things to add to it that would make it faster on a track in a 3-wheeled configuration. I like the looks of a 3-wheeled Slingshot better, but you never get the crazy fast acceleration feeling in a Slingshot because rear traction is such an issue. At some point you just hit a performance wall with 3 wheels, to go any faster you would need to add a quad kit.
Props to Bob and making this kit a reality so people can buy it. For around a $50k budget/build, this is a tremendous value compared to other vehicles with this type of performance.
You can now purchase a KTM Xbow in the US but only use it for track days. For about half the price, a 4 wheel Slingahot would be quite the competition and at least as much fun.