Hi,
I also purchased the i.MX53 QSB and had it delivered to my country (Colombia), I used I well known courier here and they gave me an estimate of what would be the amount to pay in customs and taxes and how much would their services cost.
So that way I knew upfront what I had to pay before I ordered the board.
I would recommend asking someone you know that does purchases in the US, he might probably recommend a good courier.
Also there is form you have to fill that states what is the destination and use you are going to give to the electronics purchased. My order almost got canceled because the seller only sent me the form many days after I did the purchase, that also caused the order to take along time before it was sent to the courier.
The form name is the ECS form (End Consignee Statement / End Use Certificacion). I recomment sending the seller an email requesting the form if you don't receive it in the following days after your purchase.
Good luck