I'd want to check the gearbox to see if there's any water in it. Clean the deck off and see if there's rust. Then lift it out of that pile of leaves and dirt and see if there's rust on the sides or the runners. Spin the input shaft on the gearbox to see if it turns freely. Look underneath to check the condition of the blades and the underside of the deck. Check the tailwheel to see if it turns and spins, and move it side to side to see if the bearing seems good.
Check the fit of the shearpin in the input shaft. If it's all wallowed out, that could be a sign that it's been heavily used and, possibly, abused.
Check the condition of the PTO shaft to make sure it's not bent or frozen up from rust.
As has been said, just because it's a Deere doesn't mean it's a good one. But it does mean you should be able to source parts for it.
If it was in good shape, I'd give $400 for it.