A new Haunted Mansion Open Edition MagicBand has appeared for sale only on the My Disney Experience website. This MagicBand can be purchased at a discount for renewing Annual Passholders and people with an upcoming stay at a Disney resort only. Hopefully this band will come out for purchase online and at Walt Disney World as well. The price is normally $24.99 (before discount) and the barcode SKU is 400035500344. Update: This band eventually did come out in the theme parks as well under barcode 400021267916.
This MagicBand is not available online from Disney (yet), but you can buy it from eBay online by clicking this link which will take you right to the product listings (if any are available).