1300 Euro isn't bad budget at all ! You just have to decide where to make the compromise.
Buying used (or new but from second hand) is also pretty much mandatory whether it is full PC, or just parts. Memory and Drives (SSD,HDD) are mainly where you can save a lot.
Overclocked Ryzen build might actually be faster than used Xeon builds but it depends on what you can source in used Xeon builds.
You could actually even build Threadripper system (1920X 12-core) probably as they go for very cheap (I've seen as low as 320 euro but you need to shop around). I've seen auctions/bazaar (brand new both) for x399 boards go as low as 200 euro.
Here are the benefits/compromises you will take:
- Older Xeon build - Probably loud if pre-built (HP/DELL/IBM), weak entry-level quadro card, but lot's of memory. DDR3 was very cheap, so it's easy to score 64GB memory in this option.
- Ryzen build - Cheapest, leaves money for better GPU. Better GPU---> Corona can't use it outside of denoiser, but the denoiser is cool enough. Also, bigger scenes in 3ds Max before Viewport gets slow (need more GPU VRAM). Games ?
- Threadripper build - Just as fast or faster than older xeon build. Less money for GPU than Ryzen because CPU+MB are more expensive. Probably the most ideal solution.
Memory is super expensive and you need fast one for Ryzen&Threadripper. Cheapest fast (2666+) 32GB kit's I've seen are 200-250 Euro. So 32GB is what you can get in this budget if you go for Ryzen&Threadripper. Ideally you would stick with 4x8GB so you can get full quad-channel memory benefits.