Let me shed some light on why I believe your plan to come to the US to buy a cheaper laptop is faulty.. First and foremost, if you have vacation plans, that is one thing.. Yes, it would be cheaper overall to get a laptop. However, if your plans are to only get a cheaper laptop, then you'll be spending more money than if you had simply bought it in the UK.. Here's the logic..
Cost of laptop in us ~ 2000$ US
Cost of flight to us ~ 300$ US
Cost per night in us hotel - 100$
Amount of time you will most likely spend in the US.. minumum 2 days (24 hour period). Maximum (1 week).
Cost of food per day ~ 10$ min.. 50$ maximum.
Amount of money you would have made had you decided to stay in the UK for a dell laptop. ???
Cost of food per day in UK ~ 5$ min.. 25$ maximum.. (Cooking own meals at home).
If everything works out, you might (potentially) save 100-200 dollars.. Is it really worth it??