There aren't many in captivity, but they can be motorised from ~£500
Here is a Greenspeed GT3 Folding Recumbent
with thanks to Danny Lustig for the opportunity!
With the GT3's 16" wheel, the electro-drive delivers loads of hill climbing power with a top speed of around 11mph
This was one of my toughest builds!
Finding a 36-spoke 16" rim was just the start...
With puncture resist tyre and 9-speed cassette it costs ~£150