Hello. I make the Newton trikes and conversions which you can hopefully find mentioned here:
Roman Road Cycles
Prices are mostly in sterling but I'm sure you can convert 'em, there's a useful site at www.xe.com for that. Shipping to the US is expensive though, a complete trike is likely to cot hundreds rather than tens of $ to ship, a tandem even more so.
If anyone is equipped for metalworking and knows about welding, bronze welding, and cycle engineering, I might be interested in a deal to supply data/info for them to be made in the states - the practicalities of shipping mean I'm never likely to sell many from here.