There is no
DVC discount when it comes to cash bookings. Assume you cannot borrow points from 2014-15? If not, I think you have several options to consider before paying 'the going rate'.
You can exercise your one time annual buy of 24 points. Not sure how much that will buy you at the treehouses but it is a start.
You can rent points for the extra days, from the DIS or from David's.
If you are an AP holder, there are discounts with them that you can check out.
You can check the discount sites, like MouseSavers or AllEars. I believe their specials are running through late spring currently, so you may not find anything yet for August.
Not sure when your reservation is in August, but given the 7 month booking window is opening, you are wise to look at your options now. Good luck!