Honestly, that mix is the way to go. My uncle used all cedar for his deck frame one year, said it was a waste of good money. The stuff you don't see doesn't need to be pretty, it just needs to hold up. He saved a ton on the structure and spent it on the fancy decking boards instead. Made way more sense to me.
My neighbor went all pressure treated for his fence and it looked fine, but he got splinters every time he leaned on it. He ended up sanding the whole top rail down, which was a huge pain. Sometimes the cheaper choice costs you more time later.