Currently $39.99 plus taxes at Home Depot, where it has excellent reviews.  Details from Home Accents Holiday:
 
Channel quaint country Christmas charm with this natural wicker tree collar. The sturdy metal construction delivers years of use in your holiday setup, while the natural wicker finish adds a homey finishing touch. This tree collar keeps your stand out of sight, creating a beautiful backdrop for stacks of gifts. A simple setup allows for easy assembly and the versatile design works with trees of all sizes for flexible use. Resistant to spills and stains this natural wicker.
 
Highlights
Crafted from rattan and metal for added strength and stability
Fits around your tree stand for a finished look
Tree collar measures 27 in.
Wicker look creates a rustic holiday accent
Includes 1 natural wicker tree collar