First, you might want to contact Disney and see what they are charging for the room. (They may have discounts available.) You can use this for comparison. The main difference is that you'll have more freedom if you need to cancel and you'll receive daily housekeeping.
If you rent from a member, you'll have to negotiate a price. To give you a rough idea...Checking in on August 9 and out on August 17 would require 119 points. Many members mention $10 per point as what they charge for a rental. That would run you $1,190 (no tax will be charged).
Sunday-Thursday nights are 11 points each. Friday & Saturday Aug 10 & 11 are 27 points each. A new season starts on Aug. 16 bringing that Thursday to 10 points.
The Rent/Trade Board here is a good place to start looking for members who want to rent.