Can anybody please give me the 'harmonized commodity code' from the commercial invoice that was included with your boots. The company you buy from will have chosen a code for your goods. This could shed a lot of light on what you would expect to pay.
You can find out the codes for the US here
DHL tend to deliver first and then invoice after so you may still get a bill upto a month after delivery.
We ship a lot of goods to the US and usually use the Harmonized Commodity Code 87141900 which is for 'Parts and Accessories of Motorcycles' which has an import duty rate of 0%. It is highly unlikely that customs will reclassify the goods. If I were to correctly classify them (its all open to your own interpretation) i would probably use 6402.19.90.30 which is 'Sports Footwear/Other/over $12'. This has a duty rate of 9% on the invoice total (ie goods plus shipping charge)
DHL have their own inhouse customs clearance people, ie goods dont go to seperate US Customs Agency premises, DHL are licensed to clear goods and collect on behalf of the government, so they tend to dig into the paperwork even less.
We dont currently sell the Sidi Adventures but will probably start soon...
People have correctly mentioned that you should not be paying the VAT on goods purchased in the EU unless the company you buy them from is not registered for VAT (highly unlikely)
Hope this helps a little!