I have pretty much done this recently myself.
If like me you don't have an interest in hardcore gaming. If you want a workhorse type pc then just look around for a lenovo business pc and then gut it into a new case and just chuck a graphics card in it. Depending on the graphics card you get you might need a decent psu as well. ALSO make sure you get the lenovo tower versions and not sff etc..
Something like this: https://www.ebay.co.uk/itm/363956567824
i would get, then wait for more money to buy the rest. That is a reasonable price. And can be used as-is until you get more money.
For reference, I got:
£80----- Lenovo ThinkCentre m93p i7-4790; 32gb ram; 1024gb hdd; 512gb ssd with windows 10 pro
£120----Corsair RM850x (2021 edition) -- This was brand new.
£35----- NZXT 710 case
£70 Nvidia GTX 980 ti
There was some various other items that cost £ like converters for proprietary connectors but it was very miniscule compared to the rest.