If you want just the wood look I personally would use marine ply, the more you pay the better it will be and some of the good stuff has beautiful grain. The bonus is its waterproof and is not affected by damp spots, birch ply particularly is awful for that.
For finish it can simply be oiled, or if you want to varnish a good cheap one is rustins yacht varnish. Thin it with a dash of spirit and apply with a gloss roller.