We went to Disney World as soon as school got out this year. We arrived on Saturday of Memorial Day weekend and found the crowds very managable. We used a good touring plan with "best days" information so that we were going to a park with lower crowds. If you're staying off property, you need to be very aware of which park has an Extra Magic Hour so you can avoid that park.
We stayed in a great 3-bedroom Condo at Windsor Hills. We had a full kitchen & a washer and dryer, which was great and helped save money. We paid $85 per night - it came to about $100 per night with taxes. We rented through this owner:
http://www.tonylopes.com/wh.htm
We did have to rent a car because there is a $10 per person, per day charge for the shuttle from Windsor Hills. Of course, that added $12 per day for our parking.
We also looked at the Seralago Hotel & Suites which were very reasonably priced and have a free shuttle.
www.seralagohotel.com/ However, the shuttles weren't the most efficient - some have you arriving well after park opening. It can also be hard to see fireworks, etc. That was what pushed us towards a condo w/ mini-van.
We planned a schedule that only visited one park per day so that we didn't need the park hopper option - that saved $45 per person + tax. That'll be a savings of $405 + tax for your group.
Here's a link where you can get a list of free things Disney doesn't advertise:
http://www.buildabettermousetrip.com/15FreeThings.html
Maple Leaf Tickets is a legitimate ticket discounter - no timeshare presentations or that type of thing:
http://www.MapleLeafTickets.com/?a=719