If you can pick up a AM4 board+cpu+memory+power supply for under £250 quid that could be a nice base system.
Maybe second hand with older generation hardware, but I'm looking at b550, 5700X/5800X, 32GB (preferably DDR4-3600), decent quality 700+W PSU, that sort of spec. If you can find me that for under £250, I'd thank you profusely
I'd keen an eye on the 2nd hand market, probably be some people offloading as they upgrade to the new platform.
Probably not at that spec a little higher .