I actually have been exploring this very thing!
I think the best option right now, since Apple has raised prices and Mac minis are basically impossible to get your hands on, is to build your own micro-itx machine. I actually built a mini-itx machine, but it does restrict your options a bit.
The Arc series Intel GPUs are what I think make this possible. I built a machine with an Arc b50 - it runs Gemma 26b a4b qat at around 30tok/s with their MTP head and prompt processing sits at around 500 tok/s. The really beautiful thing about this setup is the entire energy envelope of this machine sits at 120w at full load - when idle, it's at 40w and i've done some work in ubuntu to basically intelligently hibernate, which drops it to 0 watts when not in use. You can use a raspberry pi and Wake on Lan to wake the machine up for a overall draw of around 5 watts when not in use.
All in all this machine cost me 1.4k to build - but if you used micro-itx instead of mini-itx parts you could do it for under 1k - it has just 16gb of ddr5 but you don't really need more if you use models that can fit in vram.
I think it's pretty incredible that you can run an actually useful coding agent on a machine with a power envelope that is less than an incandescent light bulb. If you go up to micro-itx you can do even large cards like an intel b60 with 24gb or a b70 with 32gb and run even more powerful models. For all of these intel GPU's you'll want to compile the latest llama.cpp version with SYCL support - they are getting speedups every day, so worth staying on the edge.