I was looking at getting this Maixduino kit since it appears to be the cheapest solution that satisfies my constraints (RISCV core + WiFi):
https://www.seeedstudio.com/Sipeed-Maixduino-Kit-for-RISC-V-...
I'm not sure what's the status of programming these from Rust. I suppose that you will probably need to build your own toolchain that links the Seeedstudio libraries.