So I am thinking about getting one of the carry ons that have been much discussed on this forum. I'm not necessarily asking about the wisdom of that (although any input is appreciated) but more about what the cheapest option will be. I will soon be going to the States (I'm a UK resident), so the question is about cheapest option. Airside at Heathrow (to collect on my way back) or when I'm in the US? I will be in Schaumburg, IL if it makes a difference, and will probably head to one of the big malls there.

Any feedback would be much appreciated.