The most important thing is that you talk directly with several photographers and look at their portfolio before comparing prices, because the difference in quality is huge and it doesn't always reflect in what they charge.
Prices are going to depend a lot on where you live, the photographer's experience, and what the service includes. In general, there are photographers who charge from pretty cheap to amounts that will leave you speechless. What I've seen is that a lot of people only look at the final number and then regret it because the photos have nothing to do with what they expected. It's worth taking a good look at the work they've done in previous weddings, seeing if you like their style, how they capture the moments.
It's not that more expensive is always better, but don't hunt for a bargain at all costs either. There are really good photographers who aren't the most expensive, but they usually have a reputation and references. Ask them to show you several complete weddings, not just the prettiest photos. Also ask what exactly is included: how many hours of coverage, whether one or two photographers go, when you get the edited photos, if there's a physical album included. Sometimes you pay more for stuff you don't need, so make sure what they're offering makes sense for you guys.