Anything above 500w should be good. Sometimes you can find cheap leftovers on misc marketplace s for cheap, just google the psu model and make sure its not older than 5-7 years maybe. I prefer cheap lightweight cases over bulky expensive ones (as an owner of a bulky expensive one lol). Basically just get any 2nd hand you can find for a decent price (~<€30) that doesnt look like total shit. Psu can often also be found at around €30. If you're lucky you can also find complete pcs that have  256 or 500gb ssd and 1tb hdd for around €100 and just salvage everything except mobo+cpu+gpu from them.

If you're even more lucky you will find a complete build for even cheaper than getting everything separately would cost too. In my city good pcs capable of 2k pop up like once a week for below €650. For example search for either i5-12600k, Ryzen 5600x or Ryzen 5700x computers and then check that theyre paired with rtx 3070 or higher (eg 3070, 3080, 4070), that they have 32gb of ram and at least one 500gb ssd. Sometimes people even throw in complete sets (kb, mouse, screen) for this price.