I have old computer with dual core intel cpu 8GB RAM SSD 250GB 4870 ATI RADEON GPU and it work's good no problems and stable 3 window's
If you need only to play l2 it work flawless with i7 7700K 16GB RAM with SSD or M.2 and GPU from GTX 1060+ on full performance ! 1000$$+ (depents GPU)
For low budget and VFM is CPU i5 6600k GPU 480 Radeon 8GB with 8GB RAM and SSD Samsung 960 Evo this build cost around 600$$
You can make also build with AMD but l2 is old game and Intel have better single core performance VFM in those bulds