As someone who did spend £700 on a day trip to the Imigration office at Orlando airport in 2002 having been given duff advice, all I can add to this is get a visa, and don't try and waffle your way past the people on the desk.
(Thats not what I did by the way, I was open and honest and had emails from the school I was going to that said I didn't need a visa) which interested the immigration people a great deal. I think that is why although I was fingerprinted and photgraphed and escorted back to the returning flight I wasn't treated quite as harshly as some of the other people who were being processed at the same time as me.
Wen I went back later in the year (to AAA as it happens) I had the M1 visa and even then had a bit of a problem with immigration. Quite frankly I think that even with a visa you are still at the mercy of the guys on the desk and if they don't want to let you in they don't have to give you a reason.