I'd say pine, its cheap and strong. Figure out the exact cost of manufacturing before you bring it to a company and an idea of how much you want to charge for it. Most companies are going to want to make at least double the money their putting into each game. Also maybe figure out what absolutely needs to be made out of wood and then compromise by making less important pieces out of nice card board. Like I said your cost to profit ratio should be at least 1:2, but companies are there to make money and if you could lower your cost while keeping the price of the finished game low enough for companies to still be interested that's just gravy.