Shooting from the hip here I’d say $800 would be a good start for all new parts. You might get down to $500 with used parts.

The most expensive piece in either build is a video card. You want to be able to load the LLM file into your video card RAM.

I just got a 16gb new card for this. I can load up to 34b models on it but poorly. Anything 13b or less runs perfectly. A 12gb card would be able to run 7b models and with the right training I think 7b models can be awesome.

New 4060ti Used 3090

Mistral-7B will run on a Raspberry Pi at q04 and a little bit of patience. For good acceleration though, you'll want an Nvidia machine with enough VRAM to comfortable store the model.