Well looking at your specs if you want to use something like Redshift or Octane (you'll probably be better off with Red since it can be subscribed to with C4D) you will need either one very expensive GPU like the RTX 3000 series (if you can get one) or two cheaper RTX 2000 series ones, but on your budget that like like a no. You can always buy a couple of used GPUs like I did on eBay, or maybe you could always get a new system and pay for it in installments?
Failing that just use what you have to learn what you can and when in a better position get a better system, it will be a fun journey for you 🙂