What exactly do you mean by "getting started with FPGA on custom PCBs?" Have you made custom PCBs with high density BGAs before? Most non-trivial FPGAs (to me that means you can easily fit a decent softcore processor with space left over for your FPGA logic) will be ball grid arrays and almost impossible to DIY without xray inspection equipment and a reflow oven. You can get what you need for a few hundred $ on eBay if you're patient and lucky but even then, getting to the point where you can solder the chips reliably will take time.
If you have the budget for professional assembly, then I would start with a Digilent product that has an available reference design you can copy later. First get used to the FPGA and how it works (they are largely incomparable to a CPU or GPU except for the fact that they both have transistors). Then, design a simpler board with a smaller FPGA and work your way up to the big 500-1k pin chips.
If you have the budget for professional assembly, then I would start with a Digilent product that has an available reference design you can copy later. First get used to the FPGA and how it works (they are largely incomparable to a CPU or GPU except for the fact that they both have transistors). Then, design a simpler board with a smaller FPGA and work your way up to the big 500-1k pin chips.