I will shortly have need for a small, low power (power as in watts, not compute power) system for always-on Home Assistant use. However, Raspberry Pis are out of stock everywhere and while they can be had for extortionate prices on various auction/marketplace sites, I'm not sure I want to spend a load of money on something which might not even be what it claims to be.

Home Assistant suggest Odroid which I'd probably go for the C4 edition but it's relatively expensive (I need to add an MMC and a psu and various other things to the listed main board price)

Any suggestions? The Asus Tinkerboard looks overkill and is very expensive. It needs to be capable of running a standard Linux distro, ideally Home Assistant's own OS. Low power consumption is a definite, 2-3W at idle is probably the maximum I'd be happy with. Wifi is a bonus although not required right now - but the ability to add it if needed is essential. Some amount of expansion capability would be good if I want to add hardware sensors or bluetooth or a Zigbee transceiver or whatever. It needs some reasonably amount of compute grunt I assume but I don't think HA is all that hungry for number crunching power. The machine will more than likely be headless at first but a little bit of GPU and graphical IO would be handy if I want to stick a display on it in the future, which I might want to.

Any ideas? Oh, and also must be easily available in/to the UK.