Between inflation generally, and DDR4 being obsolete and unsupported by current desktop or server CPUs, it would be unsurprising for DDR4-3200 DIMMs to be at an all-time high even without the current DRAM price shock. You can never count on old memory types dropping to bargain prices, because the major manufacturers are always eager to migrate the bulk of their production capacity to current-generation memory.
Here the price hike was pretty instant as secondary effect of DDR5 evasion in two waves. I July and now in October.
There is usually no shortage of old working PC components as they also are avalable used and tested from people decommissioning and upgrading systems.
These are not some rare parts in normal market situations.
I made a habit of maxing out motherboards a year or two before upgrading to an new platform. This was always dirt cheap until like 5 years ago.
Yeah the cheapest time to buy old tech is always just when the new stuff has come out. That's when suppliers are trying to shift old stock at cheaper margins.
You can take a look at the 5800X3D and how it was at its cheapest about 2 years ago when AMD was winding down production and Zen 4 had been launched.
To further your point, a used 5800X3D still goes for ~$300 when you can get a brand new 7800X3D for the same if not slightly cheaper (was on sale at MC for $280). I assume the high cost of DDR5 is pushing more people to not upgrade to AM5 and stay on AM4 for as long as possible. And most people are avoiding Intel chips out of principle after the chip degradation debacle - you can see that based on how much lower Intel motherboards are even though they have considerably better feature sets than the AMD equivalents.
Main reason for Intel boards being cheap is because they're practically one and done because of Intel's insistence on changing sockets every other generation.
I wonder if semi-reliable RAM could be made to work for training. After all gradient descent already works in a stochastic environment, so maybe the noise from a few flipped bits doesn't matter too much.
Well, it kind of depends. With XMP (which is overclocking) I've found plenty of kits on Ryzen not passing memtest with the XMP settings. Different CPUs seem to be able to run their memory controller harder without error.
And then there are other factors like more sticks of ram stressing things further. I had to downclock to get memtest stable when running 4 sticks even though each kit ran fine on it's own. But that is expected as well as 4 sticks stresses the memory controller even further.
I confess I don't have any real recent experience with DDR5 though, mostly with DDR4 on Ryzen 1000-5000 series.
Even current DDR4 3200 DIMM prices are at an all time high.
These are 6+ year old chip specs now!
I even thought stuff was overpriced four years ago in mid-2021 already, but this is a whole new level.
Some sample long term data for those:
https://geizhals.eu/?phist=2151624&age=9999