Anandtech had a nice recent article on server memory types and costs: http://www.anandtech.com/show/7479/server-buying-decisions-m... (https://news.ycombinator.com/item?id=7044992). It prompted me to go through and do some math.

If you want to cram as much RAM in a server as practical, you'll currently be using 32GB LRDIMM's which currently cost ~$600 ($20/GB). Some dual-processor motherboards will take 24 of them (3 ranks * 4 channels * 2 processors) for a 768 GB total: http://www.supermicro.com/products/motherboard/xeon/c600/x9d...

(The 1.5TB description for the board presumes the soon to be released 64GB LRDIMMS.)

This would be $15000 for just the 768GB of RAM. Let's guess another $5K for the rest, so $20K for the machine. At 20GB of dedicated RAM per VPS, you can fit ~40 of them on the machine. $20K / 40 = $500. Since this ignores power and connectivity, I think you'll be waiting a while for a $5 month plan. Although perhaps you could overprovision and swap out a lot?

Viewed alternatively, the sweet spot for selling RAM does not involve putting as much of it as you can in a single machine. You'd cut the cost of your RAM per GB a lot (down to about $10/GB) if you stuck with older lower density RAM put a bunch of low price blade servers in a single box.