Keep in mind that Export Control just means you can't sell them outside the United States without the proper paperwork. It has no bearing on sales within the Unites States. For example, many Surefire flashlights carry an Export Control, yet they are still sold within the U.S. to civilians without issue.

As long as you live within the United States and body armor is legal for you to own in your state/county/town, then there is no reason you can't buy it.

With that said, if you want a cheaper and lighter weight alternative to hard plates, you can buy soft ballistic inserts. They're essentially the same as the plates, but only rated to level IIIa (so basically it covers everything other than high powered rifles). These range anywhere from $50 to $250 depending on size.

Here's some: http://www.bulletproofme.com/Briefcase_and_Backpack_Shields.shtml