How much duty tax would I have to pay...?

Here is the official government word on the subject.

The Harmonized Tariff Schedule of the United States (HTS) was enacted by Congress and made effective on January 1, 1989, replacing the former Tariff Schedules of the United States.
The HTS comprises a hierarchical structure for describing all goods in trade for duty, quota, and statistical purposes. This structure is based upon the international Harmonized Commodity Description and Coding System (HS), administered by the World Customs Organization in Brussels ; the 4- and 6-digit HS product categories are subdivided into 8-digit unique U.S. rate lines and 10-digit non-legal statistical reporting categories. Classification of goods in this system must be done in accordance with the General and Additional U.S. Rules of Interpretation, starting at the 4-digit heading level to find the most specific provision and then moving to the subordinate categories.
The "general" rates of duty subcolumn contains U.S. normal trade relations duty rates; products of some NTR countries may be eligible for preferential tariff programs, as reflected in the "special" subcolumn. Column 2 (the so-called "statutory rates") applies to countries listed in general note 3(b); the general notes set forth the rules for applying the HTS. Embargoes, anti-dumping duties, countervailing duties, and other very specific matters administered by the Executive Branch are not contained in the HTS.
The USITC maintains and publishes the HTS (in print and on-line) pursuant to the Omnibus Trade and Competitiveness Act of 1988; see the preface to the HTS for additional explanatory material. However, the Bureau of Customs and Border Protection of the Department of Homeland Security is responsible for interpreting and enforcing the HTS. http://www.usitc.gov/tata/index.htm

The best that I can tell you is to go to the I.C.E. web site and see if you can find a customs ruling on the specific types of good that you will be bringing or sending into the US. http://rulings.customs.gov/ The rules are very involved and very complicated, so I wouldnâ€™t even begin to try to give you a specific answer without knowing a lot more than what you have told us.

With the goods that you bring with you, be prepared to pay the tax when you return. Otherwise, I.C.E. will hold the goods until the tax is paid. If it isnâ€™t paid, ultimately the goods would be auctioned off.

In dealing with I.C.E., remember, if you push the envelope too far, you can be prosecuted as a tax evader under 26 USC 7201..

Any person who willfully attempts in any manner to evade or defeat any tax imposed by this title or the payment thereof shall, in addition to other penalties provided by law, be guilty of a felony and, upon conviction thereof, shall be fined not more than $100,000 ($500,000 in the case of a corporation), or imprisoned not more than 5 years, or both, together with the costs of prosecution. http://www4.law.cornell.edu/uscode/26/usc_sec_26_00007201----000-.html The safest thing to do would be to contact a customs lawyer and have him or her tell you what the procedures are in the I.C.E. district into which you will be shipping the goods. I.C.E. is like the I.R.S., each office sets local policy to some extent. And be prepared to pay whatever the tax is, which may be difficult to figure out.