Wayfair offers the Elf Stor Rolling Christmas Tree Storage Bag in Red, model no. 1021, for $33.99 plus $4.99 for shipping. That's the lowest price we could find by $7, outside of the mentions below. It holds up to a 9-foot disassembled tree.
A close price: Walmart, Discount Tommy via Amazon, and Jet.com have it for a buck more with free shipping.