I believe you wouldn’t find anything cheaper than an Orange Pi setup, but maybe I’m worng.
Edit: if you don’t have any problem about having to swap microSDs from time to time I suggest you to go for a Orange Pi Zero 3 with 4GB ram, but if you don’t want to mess around with the microSDs thing, Orange Pi 3 LTS have a 8GB eMMC or you can grab a Orange Pi 3B with the eMMC module in a bundle at AliExpress.