I have no experience with any of this, but to my knowledge what you're looking for is the Rocket Chip.[0] It's a RISC-V core implemented in Chisel. The primary FPGA target is a bit steep at around $500 [1] but there's a "small" config[2] that targets a more reasonable $190 board [3].

[0] https://github.com/freechipsproject/rocket-chip

[1] http://store.digilentinc.com/zedboard-zynq-7000-arm-fpga-soc...

[2] https://github.com/freechipsproject/rocket-chip#-how-can-i-p...

[3] http://store.digilentinc.com/zybo-zynq-7000-arm-fpga-soc-tra...