where can i buy Artix-7 or Zynq-7000 from xilinx and how much cost these products?
Xilinx just started to ship the first samples of Zynq-7000 (see webside). You may not get the first "normal" devices before 2013, I think. Price depends a lot on the quantity, but you can read of $30 on the web if you really take a lot. Google for it. If you need precise information contact xilinx or your distributor.