I know it's expensive to book at deluxe hotels. I planned a birthday vacation for me and my DH at Wilderness Lodge, I had a AP room only rate, and it was about $225 a night a couple years ago. I think the monorail resorts are definitely more expensive. The Poly and GF probably cost at least $400 a night for a studio with discount code.
Have you checked into renting DVC points for a studio or 1 BR villa? You could check into booking at Bay Lake Tower. It would be a little cramped in a studio, the kids could probably sleep well on the queen sleeper sofa, and you and DH would have to sleep on a queen bed. Or if it's in budget check out the 1BR villa. I'm guessing the cost to rent a standard view 1BR would be in the $390 a night, a studio probably runs $210 a night.
The main factor in price is the time of year, peak vs. non-peak. Months like Jan, Sept, Oct, Nov, Dec, are cheaper in general, except for the last 2 weeks in Dec. I don't know what dates you are looking at, so this is pretty general.
I've read that David's DVC rental is good.
Your family can order free custom maps at the WDW website, that's kinda fun to do.
Good luck with planning. I'm sure everyone will have a great time.