We bought annual passes and will be going 12 weeks with them. The APs were about $500 each, so our average cost is under $50 per person per week. (When we went less often, we would usually do two weeks and a 10 day base ticket, which was about $125 per person per week.)
We usually find airfare for under $200 per person.
We typically get a rental car for under $200 for a week.
(We'll drive if the total airfare and rental car cost is much more than $1000.)
We stay in nice 2BR timeshares, and our effective costs (factoring in initial costs, annual maintenance fees, exchange fees, etc.) usually ranges from $300 to $600 per week.
For food, we usually eat in the timeshare or pack a lunch, plus some counter service and off-site dining. We typically spend $300-$400 per week, which is only about $100 per week more than we would spend at home so that's what I use for my figures.
So for our family of five (including DS1, who doesn't need tickets yet), that totals up to about $1800 for a week, $2400 for two weeks or $3000 for three weeks.