You are not gonna find a real HK MP5 for a "decent" price, anywhere. The closest that you will find is a clone version.
They are cheap! Google dealer sample mp5 and you can find them for less then $1000.00. You can buy them but you will have to get your type 07 ffl. Pay your SOT , get a letter from the CLEO and its yours! That simple lol. Or move to Russia and order one