isn't floor price 0.10$ for last couple years?

Well, that's sub-$0.50. But yeah, CH32V003 is in that ballpark, and some of the cheapest Microchip and Infineon products are around $0.20.

It's almost never worth it to buy the cheapest chip unless you're making a million of something, but there are very good ones around $1-$2, and $5 is the upscale stuff.