They are quite cheap.
Each piece is about 13cm x 7.5cm, so that's 6 x 3 or 18 bases per piece, and a pack comes with 4 pieces!
If you glue the off cuts together, or have some bases which transition to earth, you can stretch a pack to use with 2 hordes!
What's more, you can cut them 4cm squares or 4cm x 6cm or larger, and glue the figures on them in a less regular fashion.