Manufacturing a chip is expensive, it requires volume.

But you can put this in altera's new flash fpga's(max10) and have a working mcu(if this fits you might even get this is in a $3-4 chip) ,but the core is only a part of the design, you need to add peripherals and memories.

This repo appears to include scripts to build this for a Xilinx 7 series FGPA. So once you buy a dev board with an Artix 7 (a quick google search shows it's about $400) and install the Xilinx tools (should be free) you can just type make and it will build the bitstream that you can load onto the FPGA.

A Parallella board is a fair bit less than $400, the Zynq is 7 series too, the scripts would need modifying a bit though.

The larger Rocket RISC-V implementation will also run on a Xilinx Zynq.

Here at Berkeley, we've successfully run our RV32I processor, Zscale, on an $89 lx9 microboard. But this took some hacking of the FPGA support repo, so it isn't officially supported.

A fair bit harder unfortunately. You only have the core here.

A regular microcontroller has a lot of necessary extras in there. You generally want modules to handle power and clock generation. Flash memory is usually in there to hold firmware. Then you need a way to load that memory via an interface. You have internal RAM for running stuff.

Debugging module like JTAG is usually in there but maybe you skip that if you use an FPGA.

Microcontrollers have various I/O like GPIO, Analog to digital, Pulse Width Modulation module, Serial Peripheral Interface.

You have to figure out your pins. The design has currently 300+ IO ports at first glance. That's not realistic.

Other posters seem to be jumping the gun and talking about loading this on a FPGA board like all the work is done. There's a lot more design still needed to get it doing anything useful (Unless your hobby is executing instructions on a CPU).

Yeah. Vendors like Altera have a whole library of peripherals like serial, GPIO, etc for their own softcore processors and graphical tools for hooking them up; I don't think there's anything like that for RISC-V yet.