Why not to use DSLRs for weddings
DSLRs are amazing tools for video, but I would not want to use one as my only camera at a wedding. If you had three or four of them, each with their own operator then that's a different situation.
Audio on DSLRs is not good for weddings because of AGC. You will get horrendous background noise. You will also lose audio continuity every time you need to stop / restart it (at least every 12 mins - and maybe more often). You will need an alternative audio recording device if you ever place to use DSLRs, to add that to the budget.
Lenses capable of 'great shots' in doors don't come cheap, and by the time you've bought a DSLR, two good lenses and an audio recording device you could easily have bought a couple of decent camcorders, giving you continuous recording from two angles so you have something to cut between.
If you are shooting from the back of the church you are going to need a long lens - something like the 70-200 f2.8L IS II. The 18-55 kit lens won't get you half way down the isle! If you plan on shooting from the front of the church, check that the vicar is going to allow it. I shoot weddings week in week out and there is a huge variation of what is and is not allowed in churches.
What will you do if the sensor over heats during the vows and shuts down? That doesn't happen on camcorders, but can easily happen with DSLRs. If you have a spare camera (more budget) you can swap, but it's too late if you only have one camera recording and you missed the vows or exchange of rings.
I've only just scratched the surface here..... seriously, for a one camera one operator shoot, the DSLR is not the best option.