I don't know how much they retail for, or if they are even legal to drive on the steet in the US, but there is one for sale with a Washington registration.
Ariel Atom 220 Left Hand Drive USA
Mileage: 2,900
Year: 2003
Colour: Red
Specification: 220 Honda, 6 speed, Road Pack, LSD, Baffled Sump, Alcon Brakes front, competition brakes rear, Adjustable bounce and rebound dampers, Eibach race and assister springs, competition rod ends, removable steering wheel, polished stainless exhaust system, stainless fixings, 17" wheel package, shift light quick release steering wheel, 3" harnesses, locking fuel cap.
Notes: Washington registration
Price: $52,500 (US Dollars)
Ref: RS
It is listed in the used section on there web site.
http://www.arielmotor.co.uk/