That is honestly a tough question to answer... you could go with a buget mind and get there and totally blow it, then you can go thinking you'll spend x amount and come out with extra (yes... it is possible). We have graduated to the ultra focused envelope system. We have collectively and honestly thought about the things that we would spend money on, with new research and years of past visits in our memory banks. Then we honestly decide how much we'll need and mark an envelope with the amount and the desired purchase. For example... DH and I always like to grap a nice iced coffee every now and then... so going by menu on Allearsnet and knowing 1 a day for is average (either or) the envelope says "coffees around the world" 45.00. Another one for bike rental for an afternoon, the candy shop, pictures from the dinner show... etc, etc. We even have extra envelopes labeled, extra with 15.00 in them for that just in case moment and each of us get 100 to spend. We have the dining plan as well, so food is not really an issue, it's all of those extras' that add up fast. We have about 1700 in envelopes for our 2 week trip this summer, but that doesn't count the ones for the drive down and back...
Now that I have babbled, I really hope this helps... it really helps us and keeps us all on track... it's exciting to work on filling the envelopes and then to get one on trip, it's almost like a present.