What are the absolute cheapest raspberry pi alternatives?

Not sure if this is the right place to post at but it seems like a good start but i have alot of questions about pi-like boards.

First what os can work on a pi and what are some neat use cases for a pi?

Just curious because i know the pi is getting more and more pricey. I know there also alternatives like the le potato priced at 35 bucks, but is that the cheapest or are there cheaper than that? Im looking for something that acts just like a computer or server similar to the pi, and where might i get said board/tech at?

Im a 18 year old student who wants to get into some tech and the pi caught my interests but its too pricey, also my parents dont really see a point to a board like the pi, so im curious of how i can convince them to let me get one? if they dont understand it.