unless they changed since last year, the rehearsal itself is free and def takes less than a half hour. really all it is, is a walk thru of how you're lined up, where to walk, where to stand, etc. that's it. no music, no officiant present, no practicing your vows or anything. only a rehearsal "dinner" has a cost, but honestly, i think that's a ripoff ... i mean how many dinners are you willing to pay for at an AI? just go to one of the restaurants with your bridal party and call it a day!
ditto what jenn said about the music ... if you are renting the sound system, they adjust the music to fit your pace, not the other way around. trust that it will be totally seamless and perfect! when you get to where you need to be, sound guy will just fade it out.