What device is significantly cheaper than and quality equal to Raspberry

I doubt you’ll find anything that benefits from the enormous economies of scale that the Raspberry Pi does. If the RPi4 is too expensive, older versions can get the job done, albeit with less performance.

A used Pi.

I asked myself the same question and snooped around for a few weeks a while ago. Didn't find anything that is a lot cheaper with the same quality. I even searched Aliexpress and the spin-offs are not really cheaper enough to justify the potential degradation of quality (I'm not saying they are of poor quality, just that I don't know).

I think Raspberry Pi enjoys from economies of scale so much that it doesn't even has boxing day deals. It's really cheap enough considering a 4GB Pi4 module only costs $72.95 in CAD. If you want there are clearance sales on pishop.ca:

https://www.pishop.ca/product-category/clearance/?sort=price...

Just a note that those clearance get cleared really quickly. I'm also thinking about getting a few second-hand Pi for a cluster I'm trying to build (which can cut down the cost further), but the thing is it's difficult to find reliable used Pi in local market.

Here is the alternative:

Radxa ROCK 3A(Quad A55@2Ghz):

- 35$ for 2GB - 55$ for 4GB - 75$ for 8GB

No wireless but you can use a m.2 wifi/bt card.