The most effective design solution may be using of PCI Express bridge. Try to find such component first. It can be PLX , AMCC or others PCI VLSI vendors.
Less effective way is to aquare IP core for Xilinx or Altera FPGA
PLDA sells prototyping board for Altera (and now Xilinx) FPGAs (In case of you brought PLDA board, PLDA provides our free PCI Express IP that only works with PLDA PCI Express board brought).
So you can design quickly a PCI Express design (vhdl or verilog) without spend time to devellop your own PCI Express IP. You just have to understand PLDA PCI Express backend interface in order to connect your backend interface.