Looking at their crowdsupply page, they did make a smaller arduino-like board [0] at a very reasonnable $59 price point.

I'm not sure if those are still available, but you might want to check it out!

[0]: https://www.crowdsupply.com/sifive/hifive1

Pretty different board. RISC-V ISA has various well-defined subsets. The cheap board is the microcontroller end of the spectrum. This CPU has an MMU, etc.