Recently, surfing the net I came across the site where people advance various ideas.
First I was interested in this:
The point is to create a SSD using USB thumb drives. We decided to calculate the economic aspect of this project. It was found that much easier and cheaper is to buy a ready-made SSD rather than try to create it with heaps of USB thumb drives.
With thumbdrives, you get the cheapest price per gigabyte if you use 7x 64GB USB thumb drives and one 7-port USB 3.0 hub (the cheapest hub at newegg). Thus, the price of such 448 GB storage is 79 cents per gigabyte while for 480 GB SSD the price is 67 cents per gigabyte.
Further I encountered this idea
The idea intends to combine old computers into network and to create iSCSI RAM disks. Looks really interesting save for one problem.
The problem is that an electric bill very quickly becomes more expensive than a SSD. Such system with capacity say of 500 GB will consume electricity at a rate of about $400/month. Again, in just one month this becomes more expensive than a ready-made SSD.