Flexi rigid is always an expensive proposition in small quantities, not too bad in thousand quantity lots, but 10 for $90 sounds entirely reasonable to me (And I have paid well over 10 times that when it got interesting).
Wurth will build you **ANYTHING**, but it will cost you, their prototype service can however produce magic (For a price), think 6 layer flexi with 1 2.4mm thick board area at one end and a 1.6 on the other side at the other with 0.15 T/G and filled via in pad, they added a clause to their flexi design rules after that one.
Regards, Dan.