How much does it cost to fix cv joint on 2005 Mazda 6?

not much mate, £20 tops, easy job too

for the 4 cylinder or v6? automatic or manual? these can be important details. I understand that the OEM warranty covers 4.6 hours of labor for "complete assembly with transfer of parts" but 10.4...

It really depends on the year and condition of the vehicle. The older and more work that needs to be done, the less it is going to cost. You could look at paying anywhere from a couple of thousand...

You should not try to repair the fulty joint just replace the entire shaft , it will run you a few hundred dollars. ( 200- 400).