Well, I'm not having my wedding until 2010 but I had a meeting anyway, as I heard that some people are even begining their planning and booking 18 months in advance (that's what we were told at our first consultation). Anyway, as I understood it, you work around your budget. We told our person our budget and what we want most of the money to go towards (like entertainment rather than decor). She took us to the Epcot pavillion, as we want a Chinese wedding at the China pavillion and she showed us Coronodo Springs, too, for a rehersal dinner option (I'm latina, my fiancee is Chinese, so we're trying to make it half-and-half). That was all on the first meeting/consultation.
If you have a budget in mind and you stress that you need to stay in that budget, they should help you out. They typically give you a 'proposal' based on what you discuss (or what is in your wishbook) which is the estimated cost of everything in your wedding (and they email it to you and also include nice pictures of the locations) and you can decide from there what to do. It's also best to ask about 'surprise costs' - things that can unexpectedly add up and that you need to be cautious about.
I hope that helps.
EDIT: Oh! Forgot to add - About chair covers and sashes: I asked about that in our meeting and I they don't really allow you to use outside vendors. HOWEVER, if you say that they're from your grandmother (she made them) or something, they'll make allowances or try and help you out. My grandmother is making runners for the tables, for instance, since she's always contributed to every wedding in the family. And we're using the table linens from the China pavillion (because it's free). The runners will add a classy and simple look to the wedding and (best of all) it won't cost us anything.