Hi -- We would like to build a pergola in our backyard, and we're trying to decide what type of wood to use. We do not want to use a treated wood because of toxicity issues (growing edibles on and adjacent to the structure), and we're wondering if that leaves us with any options other than cedar, which is out of our price range. Are fir or pine appropriate for exterior use? Would a sealer keep them in good shape for 5-10 years? We are in the mid-Atlantic and the pergola would get full sun. Thanks!