I'm with you... by the time we have our PS, we'll be at around 3 months till the wedding. If they take 2 of those months to get our BEO to us, and then we have to do the 'back and forth' dance of stripping away the extras till we get it on budget... Well... that'll be stressful.
I'm sure they have a way of handling it so you're not totally left in the lurch. Mostly, I'm going to be asking prices of everything so hopefully we can have a rough idea of the cost when we leave the PS.