The only time I went on a tour, end of HS, I believe I had the LBS pack by bike into a cardboard box suitable for taking onto the plane.

Today, at my LBS (not the same one - different states) the guy suggested I buy a $350 Bike Box.

I've had my bikes shipped cross country in the cardboard boxes. Am I really risking things by going the cardboard way again to take my bike on a plane from the US to the UK? I don't forsee another overseas tour in the near future so am not sure its worth shelling out $350 for a proper bike box (I don't have use for a wallet right now since i have virtually no money) but at the same time, I don't want to arrive in the UK and find that my bike has been damaged.

Thoughts/Opinions/Suggestions?