[andoriyu]

Well, Hifive Unleashed is a dev board with tons of features for developer, a market where $1000 is pretty okay price. It has DDR4 ECC RAM,

RPi is another story: it's a single board computer with exposed GPIO and used to be shipped with ancient GPU.

Hifive1 is more of a competitor to Arduino if you can call it that. They even have the same pinout for expansion.

They are quite pricy, like you said, due to early adopter fee. However, you gotta understand that SiFive develop their cores and unlike Arduino RPi can't just slap something that is already produced and ready to be mounted on a board.

[pavehawk2007]

I've been trying to use the Sipeed Maixduino. It's much like the hifive1 except it uses the Kendryte K210, which is a fully supported RV64GC dual-core. It even supports supervisor and user modes. It's also relatively cheap. The problem is that documentation is lacking, so I'm having to reverse engineer their BSP: https://maixduino.sipeed.com/en/