These guys might be able to help.
http://www.shelterislandmarineelectronics.com/
Raymarine has a $675 flat rate repair charge for C80's.
then you need a DSM30 module, about $500 and a transducer to plug into the module, about $200.
Also the C80 can only use an analog radar antenna. Raymarine only sells digital antennas now. But you can still sometimes find an analog one on eBay.