Tecnically, a one bedroom only sleeps 4 (same as an Inn room). So if they were preventing you from booking based on sleeping capacity, they should have directed you to a 2 bedroom not a 1 bedroom.
Renting from a DVC Member would be the cheapest way to go. A 1 bedroom (Sun through Thurs nights) would be $180/night based on a $10/point rental agreement with a DVC Member for the month of Sept. And a 2 bedroom would be $240/night (Sun thru Thurs) during Sept.
You could also go with renting two Inn rooms for either $80/night (Sun-thurs) for Sept and a standard view or $100/night for an ocean view.
If you choose to go during August, the prices go up (Sun thru Thurs):
$100/night for standard Inn
$120/night for ocean view Inn
1 bedroom : $220/night
2 bedroom: $290/night
Much cheaper than paying rack rate for these villas. Now, if you include the weekend nights (Fri/Sat), the points jump up considerably. A standard view Inn room during Sept goes from $80 to $220/night for Fri and Sat ! This is all based on the Member charging $10/point (which is usual and customary....though I have seen $9-$11/point)
Here's the DVC rent boards link :
http://www.disboards.com/forumdisplay.php?f=29
Inn room standard