Hahah! Love the soldier costume! As much as I could make the flamethrower fully functional, which it sort of will be (to a point) for accuracy, I will make sure there's something in place so that it can't be.
Now my son wants to do TF2 character for next Halloween too! Just not sure, he's not picked who he's gonna be yet. (spy might be easy)
Your mention of the Spy reminds me of the funniest cosplay idea I've heard in a long time. Go to ANY Con at all, and dress as the TF2 Spy with a paper mask of whatever appropriate character for the Con. Boom, universal costuming. =0)
Note: If your son is realllllllly little, Heavy would be adorable.
Just had a quick look, $50-$100 not too bad for an actual gas nozzle, at least I know they can be obtained.
Looking most likely to start the flamethrower just after Christmas/New Years. My son, he's 9 years old, I just recently built him a gaming PC so he can join me on servers in TF2. He's small for his age. Definitely not a build for a heavy! :lol Going to discuss further with him which character he likes best. Would like to see him choose his fav. Maybe Scout would work too. TF2 is such a great source for costume/weapon props!