Stuffing it into your basement, which is the "build your own data center" option, isn't prohibitively expensive, not does the hardware have to be. There's a gulf of prices between a Raspberry Pi and a new Dell or HP server. On top of that, getting 5 nines of uptime is costly, but we're not trying to self host Google.com here. If my personal file server goes down, my friends'll eventually notice but we're talking about a service that gets 0 rps (requests per second) when all of us are all sleeping, so no nines is sufficient. More would be great, but like you said, it's expensive.