Affordable hardware for local agents

I'm interested in a dedicated machine to run agents 24/7, as I can see cloud APIs getting expensive at this usage. Since this is just for experimental purposes and not for interactive tasks, I'm not super worried about getting a huge token/s rate.

I have a 16GB Mac mini I can repurpose, but it can only run Qwen2.5 14B, and it seems like 32B is a good sweet spot for agents.

Are there any options other than:

  1. A Mac with 32GB+ RAM

  2. 3090 from eBay for $900

  3. A CPU + fast RAM setup? I'm less familiar with the speed you can expect here

I appreciate any insights since I don't see that many posts about non-interactive use cases.