Nose
The nose is built from old cardboard, and extruded polystyrene foam. Basically, the green/blue/pink foam you get in the DIY store for insulating your home. It's very easily workable. You can carve it with a knife like balsa, and even sand it, but you can get a huge block of it for 10 euros, which is considerably cheaper than balsa, which costs a fiver for a 3mm x 100mm x 1000mm sheet.
Here, I've sealed the foam against the bodyfiller with emulsion paint. It's messy, slow to dry and seems to soak into the foam.