ch32v003

Here's the CH32v003, https://github.com/openwch/ch32v003 These are pretty low end and are fairly available at low cost. Here's a youtube of someone talking through some of the the CH32 boards, https://www.youtube.com/watch?v=Kss6WQvJbRs He talks about them being the "10c/chip" chip. Then, there is the CH32v303 https://www.wch-ic.com/products/CH32V303.html, which is the lower end of the chips that support minimal floating point and USB host/client. These ones are a bit more pricey, https://www.lcsc.com/product-detail/C5456849.html at $US1.72 each. The extra price is QFP64 (64 pins, quad flat pack) and more features on the chip, USB, CAN, V4F extension giving one instruction multiply and some floating point operations. Note that the fact that this chip uses an extension, V4F, for floating point (I think?) is part of the argument of Dmitry'

Actually, they did a huge buy of RP2040 right out of the chute, in order to get decent prices. Heck, in not huge quantities, the chip costs $ 0.70 --- not so bad. But if you want super cheap, 'standard'-type uC chip, look at the $ 0.10 https://github.com/openwch/ch32v003/tree/main

There are some MCUs that use RV32E also - the CH32V003 [0] comes to mind. [0] - https://github.com/openwch/ch32v003