I know that this is probably late, but if you want absolutely cheapest the best thing to do is book off of Hotwire. We have never gotten a place that we hated, and the prices are about 1/3 to 1/2 off.
In location type "Disney World" and when the results come up the best places to search in is "Lake Buena Vista" for the nicest, "Main Gate" and "West of Disney" are also good; finally "Kissimmie" will usually get you the cheapest rooms. Also, subtract a half a star from the rating for realistic expectations.
Remember, things change all the time based on dates. These results are from my general experience. We have used this service about a dozen times over the years. I have only been disappointed once, but management gave me a free night stay on a later date so it was alright.
I have used Hotwire to book a one bedroom condo, upgraded it directly for a fifteen bucks a night to a three bedroom, (Hotwire had no knowledge of this) combined with my Military discount to get a week vacation for four adults and four children (granted, two of them were under three) for less than a grand. We went during the offseason and spent less than 300 bucks for the condo. We shopped at Aldi, ate out of a cooler in the parking lot for lunch, cooked our own breakfast and late dinner. The military tickets were I get in free and I could get an additional four for 100 bucks each. I had to pay for one Child ticket. I am not sure though, it was two years ago.