Mailing from the US to Soldiers deployed is like mailing to anywhere else in the states...the price is the same as if you mailed someone in another state.
For us in Germany because it's only military postal workers who handle packages, it's free...but everyone else it costs. So if you send a care package priority it's going to cost you, well what ever priority is now (4 something I think). Once the package gets to Germany they're then shipped downrange. Once they leave the East Coast they're in the Dept of Defense's care!
Letters and postcards are the price of the stamps! If I am not making any sense, please feel free to email me anytime!!!
Oh and if sending a package, you do have to fill out a claims form. You can get a handfull at your post office and then when you're filling up the box, just write things down as you go!