Very easy to fix.
Last year, 1 month after I bought my CX-5, My taillight was STOLEN (the one on the hatch). someone pried it off with a screw driver, dented the hatch itself, and broke off the screw on the tailight so it's useless to them.
There's an access area inside behind the hatch, open it and I believe it's 2 screws. Un do them, and pull the light off. It might be hard because of the "sticky" type water seal.
The hatch light is about $90. Don't order the water seal, it's already on it. I made the mistake and ordered the water seal, about $9 pre cut/sized/etc.
The corner taillights, with actual brake lights in it, that's pricey. $200 each. So you're looking at about $300 to fix for just the set of taillights.
The real tail light I didn't have to replace, but it's just as easy to do.
Here's the thread I wrote about my stolen taillight:
http://www.mazdas247.com/forum/showthread.php?123831013-Advice-Needed-Trunk-Light-Stolen&highlight=