I use a lot of recycled wood from variety of sources.
Drawers from old furniture are a good source of a variety of thin timber.
Beech sewing Machine bases like this are common, and aren't worth mending, but are a good source of solid, well seasoned wood.
Recycled materials aren't necessarily cheaper than new ones, when you take into account the time spent preparing them, and removing nails and screws, but there are a lot of advantages.
Often I'm using material which would end up in landfill, or be turned into chipboard and I have built up a stock which would be expensive to match in new wood, and may not be available from renewable, or ethical sources.