Sadly, the days are long over when companies would send free CDs in the mail. So if you're looking for inexpensive basing options for your scenics, where can you turn?
You might take a look at crafting supplies, particularly wooden shapes. The pack shown above contains ten pieces of wood, found in the craft aisle at Dollar Tree.
These five-lobed shapes (flowers?) are stamped out of 2mm-thick wood. Some edges are rough. The wood is thin enough that you easily could snap it in two.
This 28mm zombie fighter (above) gives a sense of how big these are. More than 80mm across or three inches.
And if that's not big enough… they make a larger one out of plywood that's about nine inches across. Comes with a bit of twine to hang it with.