Orbitz has rooms at the Poly for less than that.
I checked the weekend of 7/25-7/28/14. Using the code DISCOVER, garden view rooms at the Poly are coming up for $353, including tax. GF garden view are coming up for $398/night. If you were to go through ebates, you would get an additonal 2% back as well.
Free cancellation until 5 nights prior to arrival if you find a better deal elsewhere. The only catch is that you would need to pay the full amount at the time of booking. Disney would only make you pay for 1 night as your deposit.