I'm using the SW airlines Visa and Rapid Rewards to get free flights. As others said, it was like 50,000 points after first purchase. That's worth about $833. Mine has a $69 annual fee, but I get 3000 each year to help offset that cost. I'm up to over 67,000 now. I've added to my points by doing surveys through e-Rewards when I have the time. You can only do that through an invite, which I got by email. There really are a lot of opportunities to get more points.
I also have a Disney Visa through Chase. I put "everything" on it and pay it off the same month to avoid fees. I currently have almost $400 from that.
If you stayed at POP or one of the AS, you could
maybe do it. If your school district starts after labor day, they usually offer free dining the last week of August and it's the second value season. My DD just started high school, so that's one of the times we're currently considering (although it sounds hot!)
If you rent DVC points, I think from the times you're considering Thanksgiving would be best (???) But airfare would be crazy. You can use this to figure out points needed:
http://www.dvcrequest.com/PointsCalcNew/PointsCalc.asp
Our first trip with the kids in 2006, we were on a tight budget and had no dining plan. We stayed at All Star Sports. We saved on food by bringing some in our suitcase -- (pop tarts, bread, peanut butter, chips, granola bars, trail mix, juice boxes, etc.) We got refillable mugs and used them to carry drinks with us to the parks (in capped "water bottles" that we brought.) We ate breakfast in our room and packed a lunch and snacks for the parks. We ate one QS meal a day, the portions are enough to share; used the Planet Hollywood voucher for a sit down meal. It wasn't bad.
I found that money saved using ME express and Disney Transportation (no rental car or parking fees) offset the savings of staying offsite.
I didn't mean to write so much
Good luck planning!