DVD Inbox and Cafe DVD is $20/mo for 2 discs at a time, with unlimited discs and a 5 day guarantee. 5 days to get your DVD doesn't seem great. They have cheaper plans but limit the number of DVDs you can take out.
Netflix was revolutionary because they shipped very eagerly and they charge $15/mo for 2 DVDs unlimited. And I think their shipping took 2 days. They shipped as soon as you shipped yours back so if you were diligent you could prob have close to a movie every night. Incredible service.
I guess the economics just isn't there.