If its just for messing about and you want to go super cheap then maybe consider an Asus Chromebook miniPC. They vary in price / performance but if mine is anything to go by, are well made and last forever
My CN60 has 4Gb RAM and a Celeron 2955 processor, I upgraded the SATA III 2242 SSD to 256 Gb. To run alternative OSes you need remove the write-protect screw, takes 2 minutes.
Has built HDMI out and Displayport, built in LAN and wifi, very quiet, plenty of USB ports, tiny form factor.
I used mine as a media player for a long time running LibreElec, then had Debian on it, now running Lubuntu fine
Killer feature is you can buy them for less than £20 on ebay, SSD upgrade will be another £20 mind you ...