Depends where you are going! I bought my Navman 5500 and super-wide C Map from Cocoa Beach , Florida last year and had no difficulty with the purchase, or coming through customs (only got charged VAT) Someone on same flight who tried to escape duty had a £3000 camera system confiscated!
I would add that there seems to be a lot of pricematching in the US amongst the major firms like West. They have invested heavily in their brands and support them quickly against any suggestion that they aren't competitive.
I bought a Lowrance unit some time ago from West - at the advertised BoatersWorld price!
You don't say where you will be, but take a look at getfeetwet.com (courtesy Jon Bailey). You probably won't be able to mail order/web order unless you have a US credit card.