[HELP] Cheap setup for pure 4k photo editing

Right. Screen-sized image files don't require more than any old cheap laptop.

Assuming you're thinking of heavier lifting than that, while still on a tight budget, build something around a mid-range i5 and a 500GB M.2 SSD. Don't spend too much on the video card, that makes little difference.

M.2 SSDs are a bit expensive compared to traditional SATA SSDs, but you more than make up for that because they're crazy fast. This means you need less RAM, which is also expensive. You might even get away with only 8GB RAM, although 16 would be better.

In Photoshop, the main bottleneck is I/O - moving large amounts of data around. That's the whole memory subsystem - disks and RAM. Pure number-crunching isn't as critical.

4K is 8.2MP even iPhones capture 12MP images  many cameras capture 16MP and 24MP images are you sure you want to discard that much detail?