If your motherboard supports crossfire, a good GPU is the R9 270, Non-X edition. That is around $200 USD I believe. You can CF it in the future, but if you're deciding between 2 cards or 1, go with 1 for now.
my MB have to pcie one of them 3.0 and other is 2.0 so are there any different or issue ill have when i cf
It's probably a PCI-E x16 Gen3 slot, then an x16 Gen 2 Slot, which equates to an x8 Gen 3 slot (If that makes sense)
Regardless, you won't have any issues, as you can change the PCI-E 3.0 slot to run in Gen 2 from the BIOS.