tbh i would just not bother with it and go straight to getting something decent even tho ddr5 prices are pretty bad.
#Buying a Used PC, to convert into a newer build
junior wing
plain wedge
Not sure about in the UK, but here in the US Facebook Marketplace has quite a few sets of DDR5 ram for sale at decent prices compared to new. I would suggest a new build all together if you are already considering a CPU, MB, and Power supply upgrade for the one you are looking at buying. Selling the old parts including the 1080ti's may net you less than what you'd expect/ be a slower process. I see plenty of used GPU's in the used market here and they sit there for quite a long time