It requires some clean-up, but cans of beer/soda are pretty fun to shoot.
They "react" a little more than clays, and can usually be had for around $0.50ea. Even less if you can find a place that sells expired beer.
I quite fancy one of those duelling tree's i've seen on Hickok45's channel, though it looks to be about $350 for a 'normal' one from Salute Products
For anything made from steel, try to find a local welder. They'll probably be able to make it cheaper, and you'll make a new friend. Not having to ship a 80lb package cuts a lot from the final cost.