Another way to get cheaper timber is wait until the local supplier has got to the end of the new stock of PSE planking and you will often find with the modern kiln dried wood today, lots with cracks and twists which get rejected by the punters.
I bought 25 meter of 200mm by 20mm the other day for a fiver and made all my hive frames and other things from if.
If you get to know the chaps well enough they will normally keep it for you for their tea fund etc.