G9 hps or 13th gen poweredges are a nice sweet spot in hl pricing. G10s and 14s and up are going to be around 1K starting because of the cpus and they are still pretty new. Xeon E5 v4s are in a nice sweet spot for cpus and you can get a lot more use than what you have now.

Pickup the cheapest HP Z440 you can find (~$120 for a barebones) grab a 12 core e5 2650 v4 for $5 and as many 16gb ddr4 ecc dimms as you wish for $12 each (all current eBay prices) it’ll idle under $100w running a few VM’s

I have 2 hp g800 sff i5 4th gen @3.4ghz a qnap nas for storage, 2 rpi 4 and an odroid m1 as a docker swarm for all my services a modem a router and my switch and I’m having around 100 watt usage for the whole cluster.

So i think an SFF pc will do the job fine and meet your power and computing requirements.

Cheap second hand gaming set up/workstation will be more than powerful enough for your use case and shave off a lot of power at idle, aim for the newest CPU you can afford without investing too much into the GPU ideally

I would look into something of HP G9 or Dell R730/R630 range. These will be more power-efficient and you should find something within that price.