At Hollywood Studios you're on one of the two patios at the back of the amphitheater. Both have a $250 venue-rental fee. There's a $750 food and beverage minimum, and menus range from $20-$27 per person. There's also a $75 setup fee, and you will be required to charter transportation at about $400 per bus that seats about 50 (if you have fewer people, you may be able to charter cheaper transportation).
In Epcot you pay a site fee ($250-$575, depending on location) and then a minimum of $22 per person for food and beverage. There's also a $75 setup fee for any location but Upper UK, and you are required to charter transportation at the same rates posted above. UK and France parties *may* be allowed to skip the transport and have everyone meet at the International Gateway and walk in, but that's at Disney's discretion.
Also, both parks have a $12.95/pp viewing fee for any guest who doesn't have park admission.
Wishes parties at the Grand Floridian Marina have no site fee. The food-and-beverage minimums are $1,500 for the Marina or $500 for Sago Cay Pointe. Grand Floridian catering menus range from $27-$60 per person, but you can customize a menu to be less per person as long as you meet the food-and-beverage minimum for your site. You also don't have to pay viewing fees or charter transport, so this could be your cheapest option. However, you can't hear the music to the fireworks, and you are looking at a side view of them. If you want the music piped in, it's about $800.
All these prices are exclusive of 6.5% sales tax and 21% service charge, so figure that in too.
