I didn't realize "sturdy" wasn't in the regs I just learned something too!
The plastic case your gun should come with is sufficient as long as the gun is locked (trigger or cable) and then the case is locked. A padlock is not required.
I bought my handgun from P&D in Edmonton and was worried about the rules for transport via plane and mine was fine. I asked lots of questions in the store and over the phone of the airline (2 airlines by mistake actually).
It was transported in the factory case, trigger or cable locked (I don't remember which), a small suitcase lock on the case and a cable lock around the outside handle.
Again if you can lock the gun and the case your golden.
You don't need to buy a new case unless they're giving you a crap one with your gun, in which case you should sweet talk them into gifting you a nicer one...
Edit: If they really want to force the new case purchase read your receipt about their return policy and if you can get ALL of your money back, no restocking fees etc, tell them you really can't afford a case right now its just not in your budget so I need to return the gun and wait a few months... see if that makes them want to play ball. Don't get strong armed.
