I thought I'd chime in here and give my perspective. I too am am a professional wedding photographer and I'm based in LA. We travel all over the world photographing weddings and I photographed several in the Cancun/ Puerto Morales area this year. There is really no such thing as one price fits all when it comes to photography, so we almost always customize a package based on what our clients desire. It's rare to find that two couples want exactly the same items, time, prints etc. so we give quotes on an individual basis.
But to hear that the "top photographers" will never negotiate surprises me. For instance, I may not negotiate my creative fee much, but I've done things in the past like throw in a Trash-The -Dress photoshoot or even waive my airfare to get down there if I wanted the job! And I think this is a testament to those of us that love what we do. Local vendors work differently that flying in your photographer. Locals are almost always going to be less expensive especially since it's one day for them to photograph your wedding and often 3-4 days for the photographer you are flying in. But what I always remind my clients is photography is the most important vendor you will have. They are the only vendor that will be by your side your entire wedding day, so you should not only like their work, but also click with them. After all, the pictures will be all you will have to remember your wedding by, and I truly believe you get what you pay for when it comes to photography.
When researching your photographers, you will most likely find pricing to be all over the place. Some charge by the hour, some charge by the package, some include an album and perhaps CD, some do not. Those who charge more are often basing that rate on their experience, level of professionalism...(like returning phone calls and emails within 24 hours), quality of products sold and their level of artistry. And hopefully they have a great written Guarantee! I recommend not paying in full before the wedding date, and I also recommend asking the photographer what their guarantee is. So many couples don't even think to ask this and IMO, it's the most important question to ask. What happens if their gear fails during the wedding, they are late or you just don't like your pictures? I've heard horror stories over the years, so ladies please if you do nothing else, ask that one question.
We all want a "great deal". I'm shopping online right now for one of my wife's Christmas presents looking for one! But 50% off your wedding photographer isn't a deal it's a red flag! I do like the free shipping though!