The wife gave me a project of building some things around the house and decided MDF was the best material. I required 2 sheets of 16mm and about 4 sheets of 12mm. After ringing around a few places the best deal i could get for 18mm MDF was $29.90 (one place wanted $53.00 and another $57.00).
After picking up the trailer from work, and taking a back way to the hardware shop I saw a sign out front of a cabinets maker "CHEAP PACKING SHEETS", well a quick U turn and after checking out the 16 and 12mm sheets i bought 2 16mm sheets for $10.00 each and the 4 sheets of the 12mm for $5.00 each.
They were slightly damaged in a couple of spots from the strapping - but for what I was using them for they were perfect.
I have also been told that the LAMINEX group - if you have one close buy will actually give the packing sheets away.
If you require some MDF of particle board for a project it may be woth while checking out the local cabinet makers for packing sheets.
It saved me a few dollars. Just becarefull as the sheets may not be perfectly square either.