As an addendum to my previous posting, I would be very surprised if a trike conversion kit (converting a trike to the standard English trike form) cost $850. There isn't that much to them. The kits I sold had three parts; an axle assembly w/hubs, two bolt-on rear stays w/clamps, and a hanger for the rear derailler. Of course, it may be that no one makes them now. I haven't gone to the links given by others yet but there is a kit available that creates a trike with two wheels in the front. THAT kit may cost $850.
Paul Patzkowsky Longmont, Colorado