A Board Material that can be used to a good effect and one that does not need to have any expense attached to acquiring it for being used as a trial is Chipboard.
Chipboard is produced in different compressions for the particulate.
A Sub Plinth produced from a not too compressed Board will be one to show a difference that is perceivable as an improvement.
For myself it has been very effective as a Tier used under a Speaker, but this will also be useful under other devices.
If an individual wants to pretty up the raw material, then this will add a cost.