Last time I took a couple of small bags of Twiglets, they were either 2 or 3pp each, I forget. But you can't eat a massive amount of Twiglets (I can't anyway), so I wasn't left feeling as short-changed as if they were other crisps/snacks.
Another good idea if you want something a bit more like popcorn is caramel Snack a Jacks, they're probably the closest (and nicest) thing you can get to a bag of toffee popcorn!