You can read a little here about the trike. If this is correct, the builder used the same frame as Jerome Hediger (US importer of Greenspeed trikes) did for his Trimuter trikes. He had an agreement with Greenspeed to buy the frames and build them in Illinois. That would make the Scarab similar to the Greenspeed GTO. Hediger no longer makes the Trimuter. Greenspeed stopped making the GTO model so it may be the reason the Scarab website hasn't been updated since 2011.
It's very difficult to place a value on something that is so rare so there aren't any comparables to use as a guide. The genuine Greenspeed GTO is still sought after but prices vary a lot. Only two were listed on Bentrider in 2019. One sold for $1500 and the other did not have a price listed in the ad so there is no way to know the price. One identical to the one I own sold in Phoenix about two years ago for $750. That was a steal.
Why no Scarab Trikes for sale? 10/16/2009 https://www.bentrideronline.com/mess...ad.php?t=54136
Hediger Trimuter Trikes https://www.bentrideronline.com/mess...ad.php?t=69293