I’ve been shooting weddings for awhile (for someone else) and I have learned a couple of thing about this subject and unfortunately by trial and error.
First of all, like they said above, go with a wireless lav mic. Hopefully your camera has multiple inputs so you can separate the lav mic from the rest of the wedding. Your better off turning it on, setting the level and not touching it again. You’ll be recording everything including what is said in the restroom before the groom comes to the alter, but since it’s on another channel, you can turn it down in post until you need it.
Second, get a lav mic that is omni directional!With acardioid you’ll never hear the bride. You’ll need to be monitoring the ceremony anyway so at that point you can turn the gain up to hear her.
Keeping it on the cheap side you can get a wireless lav from Nady or Gemini for under $100. Remember you get what you pay for, it’s a starting point though. The problems with the cheap ones is interference… If you’re near a highway you’ll get the CBer with his radio powered way up, you might walk into a church on the same freq.
Good Luck!
