Ampere Servers? Yes. Cheap? Maybe. I'm seeing Dell r740's for under 2k (nearly barebones, minimal RAM, no GPU, no disk storage), and they are compatible with ampere cards, but they're definitely not coming with the Xeon Scalable CPUs.
Ahh, gotcha. Those are fairly new to the market, aren't they? Depending on how many of the big boys are deploying them, I wouldn't expect to see a flood of decommissioned hosts for like 3 years minimum. Depending on production numbers and whether there's a supply chain crunch, you might start seeing the RMA refurbs hit ebay mid next year.
I do recall 5 years being the most common length of a racks lifecycle. If you know who has been using them in their fleet, I'd start keeping an eye on liquidators a full quarter after that companies 5 year deployment mark. Depending on the service provider, it can take a while for the decommissioning process to be finalized by financial depts and for assets to be released for sale.