For a while, and I think even still today, the cheapest linux thing you can buy that has USB ports, wifi, and a power adapter are those Rockchip CPU powered Android TV boxes that are super popular from aliexpress and the like. There were people getting pretty mainline Linux distros on them. They have all moved on to be more expensive now (with 8GB RAM and way more cores than needed), but if you look back at ones from a few years ago you can find ones that were 1GB or 2GB of ram with a bit of eMMC storage and a quad core arm CPU roughly equivalent to a Raspberry Pi 3 in performance. Unlike a lot of these linux microcontroller-sized boards, you got barrel jack power in, HDMI video out, wifi, usb ports, an audio out, and a nice case for it. What you lack is exposed GPIO usually. At one point you could find them for around $24. FOr people who don't need the GPIO and instead want to use a keyboard/mouse/monitor with one, I think those are often better options than the SBC market embedded-style dev boards. I think you still can if you look hard enough.

One of these days, I will do a project with linux on a cheap Rockchip handheld game console. Many already have builds of rocknix which is a retro game focused OS with mainline latest kernels. Many of these can be had for < $50 and boot from sdcard, and have wifi and bluetooth.

> They have all moved on to be more expensive now (with 8GB RAM and way more cores than needed)

even the exact same model that I use for, ahem, iptv purposes has ballooned in price by 50% over the past few years, despite no design upgrades/changes :(