Can anyone make a device that uses pcie?
You only absolutely need to pay money to PCI-SIG if you need your own vendor ID. If you’re using an FPGA, you can use the FPGA company’s vendor ID (for Xilinx, it’s 0x10EE).

Otherwise there’s no IP licensing to speak of. The specs are free download for PCI-SIG members, non-members pay a fee for them.