Wow! There’s a lot out there for wedding cakes! But before you contact a baker, or wedding cake designer I guess they are called these days, it’s a good idea to take a few things into consideration. (My daughter is planning her wedding for next year, so I find all this information very useful since it’s been a long time since I helped plan a wedding.)
Most brides-to-be, and her groom too maybe, will have a theme idea they will prefer for the cake, but that may have to wait until the other, larger issues have been resolved. In other words, the cake doesn’t come first. Anytime after the wedding date is set, the cake can be ordered, unless it’s years away, and provided you already know what you want and how big it should be.
Cake choices have virtually no limit, so your budget, guest count, and color scheme will all be requirements first off. Once you have a very good idea of what you like (save pictures), choose a cake maker near the place of the wedding and set up a consultation and cake tasting (yum) to see if you feel comfortable with their abilities and agree with their price quotes.
Most cake designers would like to have the order at least a month ahead of time and they may need more time if you get married during their busy season.
As far as cost, it’s impossible to say, but The Knot has a post with helpful general info about what is pricey and how to cut costs.
The post at My Sweet Wedding gives some good pointers from a cake decorator’s point of view.