Oh, the woes of a low ranked witness in a bear market. I'm not going to waste your time with a long-winded story as it did take a fair bit of trial and error on my part, so I'll get straight to my conclusions. To be clear, this is not a recommended config, but a bare minimum that has proven to reliably sign blocks as a witness over the last 3 weeks. 

- Any dual-core CPU post Sandy Bridge (2011, 2nd Gen Core) 
- 2 GB RAM 
- Any modern SATA3 SSD with 400+ GB. Hard drives will not do, NVMe preferred but optional. Affordable consumer grade SSDs like Samsung 860 EVO work just fine. 
- No graphics card or any other special hardware required. 
- Of course, a reliable network with 10+ Mbps. 

So, the caveat here is that this setup will *run* Steemd on an ongoing basis, but setting up will be a glacial process on the above system, because shared_memory is stored on disk and the CPU is slow. So you'd have to do that on a different platform. 

More specifically, replaying on something like the above machine takes 2-4 days. So, you would temporarily have to rent a 64 GB RAM instance with a high single thread performance CPU (i.e. anything 6th gen Core or later) for about 6 hours. These don't cost much, but require a bit more work. Build steemd, cli_wallet (or use Docker), sync up shared_memory, block_log, then compress and move those files to your el-cheapo server and... voila! This process would have to be repeated every time there's a major hardfork or replay required, but these are usually very rare (think once or twice a year if all goes according to plan [which may not, like HF20]). Or, you can just be patient and disable your witness for a couple of days. Finally, we know Steemit, Inc. is working on scaling solutions with MIRA, so maybe by the time the next hardfork arrives we would actually have fast replays off SSDs alone. (According to @andrarchy, that's [still the goal](https://steemit.com/steemit/@steemitblog/engineering-update-all-team-meeting-condenser-split#@andrarchy/re-truth-be-told-re-andrarchy-re-raycoms-re-steemitblog-engineering-update-all-team-meeting-condenser-split-20190308t164156399z).)

So, how much would a server like the above cost? You probably already have a PC or laptop that can do this. Or, if you were planning to rent, if you look you can find something for <$10 per month. At that cost, it'd be feasible to run a witness node all the way down to #200 or so. 

Once again, to be very, very clear, this is not a recommendation. It's an academic study of what the lowest configuration is required to run Steemd as a witness. That said, if you're looking into being a witness and don't have the shilling skills required to make it (I hear you), this might be an option worth doing your own research for.