Read the linked article? https://docs.xilinx.com/v/u/en-US/microblaze-quick-start-gui.... It's an Xilix FPGA design, so a Xilix dev board is the where to start ...

You will find the entry-level boards here. (ranging from $150 to ~$4000)

https://www.xilinx.com/products/boards-and-kits/cost-optimiz...

I'd go with any cheap[0] xilinx one that supports microblaze soft CPUs.

If all you need is a RISC-V softcore, then there's plenty of options outside of Xilinx ecosystem. I like anything yosys/nextpnr supports well.

0. https://www.joelw.id.au/FPGA/CheapFPGADevelopmentBoards