Just looking at the current premium sale page for Europe, a Club Europe return to Thessaloniki is £289. But you can add 7 days premium car hire for a total of £1729 £1440 for 7 days car hire seems a bit much to me!

I guess it's just a glitch in the system, but it stays at that price if you do a dummy booking.

(avisba.com comes up with a more reasonable 200 quid type price for car hire as I would expect)