Assuming the need to go to multi-layer for the BGA part, that looks like it will be a very expensive board. You might look at a part such as the XC3S500E-4PQG208I which is in a 208 pin PQFP package. The FPGA is a bit more expensive but the PCB will be a fraction the cost if you can keep it to 2 layers. Also at least when it comes to Seeed, the cost of the board increases rapidly with size. 5cm * 5cm max is around $1/bd, 10cm * 10cm max is $2.50/bd, while the next size up, 15cm * 15cm max is close to $9/bd. If you can manage to keep it within 10cm square then the bare boards are ridiculously cheap.