Cost is a major issue for me too, so my wedding is no where near what some of the girls on here are doing. Yes, some are having extravagent but very beautiful weddings....that's just not in my budget unfortunately.
I may get some backlash for saying this, but I actually disagree with the advise to hire a travel agent (just my opinion). If you take the time to research and really dig using the various forums and google searches, you can find all kinds of options and determine the least expensive choice that still meets your standards.
For me, Playa del Carmen was still too pricey so I started looking in other areas. I found a place in Akumal that does very low-key, laid-back beach weddings (just my type) and the hotel rates were incredible. Yes the location isn't as opulant as some of these resorts.....but it's nice....
So I guess I'd say maybe be open to the idea of making some compromises to get what you want (beach wedding with family). feel free to PM me if you'd like info on what I'm doing, but I'll post full reviews w/ pics after my wedding....