Found mine was cracked after having the car 12 months, figured I would try and fix before buying knew and it can be done!
Front surround trim pulls off, carefully and I'll unclip all the way round.
Next you need to remove the sliding door, there are two metal springs, one top and one bottom, subtle so don't loose them, there also greesed for smooth running.
Once the door is out, the broken mirror can be removed, it's just sticky back adhesive. I used a small 15cm plastic ruler to free it.
Replaced broken mirror with a plastic one cut to size online, 70cm x 130 x 3mm thick. Cost me about £7 delivered.
Stick new mirror into the right hand side, gap to the left is space for reinstalling the slide door.
Reinstall door, you want to locate one of the 'legs' in it's runner and then push/pop the second into place, greese runners, clean up excess and check smooth running.
Reinstall surround trim, will only fit one way be sure to align clip positions, click click click all way round, done.
Easy and about £120 cheaper than a new sunvisor.