Probably the main thing that affects what a photographer charges is time spent at the site.  Usually a photographer will offer different packages according to how long he is at your wedding and/or reception. This might start at just 1 hour for a smaller, civil ceremony at a justice of the peace and go up to 12 or 14 hours to cover the bride getting ready in the morning to the couple leaving the venue at night.
 
The number of factors that determines wedding photography prices is:
 
1.            The amount of time (how many hours) the photographer needs to serve.
2.            Number of photos he will take.
3.            The size/quality/brand of wedding album;
4.            Any additional products such as framed prints, proof albums or DVD slideshows.
 
Be sure you understand everything the photographer is going to do and read the contract before you sign it.
Source: http://www.brides-guide-to-wedding-photography.com/budget-wedding-photography.html