How can I reduce this €4,500 Rust gaming PC to around €3,000?

If you still need to cut further, a 7800X3D paired with a B650 board is worth considering, especially if it’s substantially cheaper in Slovenia. The 9800X3D is faster, but the graphics card and memory changes will make a much larger difference to the total budget. You could also assemble the PC yourself if you’re comfortable following a guide, although paying €60 for assembly is reasonable if you don’t want the risk.

You can cut the memory from 64GB to a 32GB kit, ideally 2x16GB DDR5-6000. That should be enough for Rust, OBS, and normal background applications. The listed RAM price is especially out of proportion, so shopping around for a cheaper kit could save a lot without affecting gaming performance.

Two 2TB 990 Pro drives are unnecessary unless you already know you need 4TB of very fast storage. Start with one reasonably priced 2TB NVMe SSD and add another later. For games, a cheaper NVMe drive will feel almost the same as a 990 Pro while costing much less.

The biggest saving is the graphics card. A 5080 is very expensive for 1440p Rust, so look at an RX 9070 XT or RTX 5070 Ti instead. Both should be plenty for this resolution, and the 9070 XT is likely the better value if you don’t specifically need NVIDIA features. Keep in mind that NVIDIA’s encoder can still be appealing for OBS, so compare local prices and recording quality before deciding.

The motherboard is also more premium than necessary. A solid B650 or reasonably priced B850 board will handle an X3D processor just fine, so compare features rather than automatically buying the expensive Tomahawk model. You could also install Windows yourself and avoid paying the full shop installation price for the operating system; use a legitimate license or activate it later.