The N3350 ones are the cheapest, they go for around $90 on Aliexpress. Finding a used one for $50 isn’t all that difficult either.
Before RPis went up in cost they were $35.
For $35 you didn’t get a full computer. You still needed a case, a power supply, a USB powersupply, a fragile SDcard and a stupid microHDMI cable. And that $35 is only for the 1GB model. The miniPCs in contrast come with everything included and even the cheapest models have a 64GB SSD and 4GB RAM.