Unfortunately, unless you are donating the wood to a place like Habitat for Humanity, you're going to have to pay to dispose of it. The good news is that most landfills will take wood for a nominal fee. You can also check with your municipality to see if they have any special regulations for disposing of wood with nails. If you live in the UK, as long as it is wood from a residential property you can take it down to your local tip and dispose of it for free.