I'm in the process of making a queen size mission style bed out of oak.
I think I spent about $500 on the wood, mostly S2S. Tools - make sure
you have some mortise chisels or a drill press + forstner bits to make
As far as plans, I have the plan at the link below (or DAGS for mission
bed plans and pick one you like). If you're spending several hundred
dollars on wood, and probably a few hundred more on tools you just
can't live without, the $12-17 spent on a detailed plan for a
complicated project is worth it in my opinion, even if it's just a
starting point. The plans I have include details for how to expand to
king size or reduce to full or twin. I've modified them slightly, but
it sure helped to have everything laid out for me.
Several other places have the same plan - "Classic Bed Plan"