In 2006 when I got my first c5 off ebay for around £280 , Sinclair Vehicles ( Adam Harper) was selling new boxed c5's for £1400 , although they did have all the accessories included. In comparison the price for these four on Ebay isnt that far off the mark.
But as Kamil says, once you have an unused C5 you're pretty much snookered.....if you use it it devalues by a massive amount ,so keeping it pristine and unused is the only way to preserve your investment.
Thats why I sold on my own unused c5.. and choose to run around in ones I built/modified/repaired myself