Olympus XD Card & Reader buying advice needed - UK or US?

Hi Folks

I'm going to the US next week and I'd like to buy either a 128 or 256mb xd
card and a reader, for my Olympus C765. In short will I get a better price
buying duty free before leaving the UK or when I get to the States? For
various reasons I won't bother you with, my only real option when I get
stateside will be a quick purchase from the airport. I'm aware of the
warranty issues if I buy in the US.

Many thanks in advance for any info or advice

JonB