rack mounts are for companys, it makes no sense for a home user to have a rack mount server, when its the same exect thing as a tower, no diff at all exect the size and being able to put like 20 of them on a rack.
renting a file server for 20 bucks a month when you can use a 200 dollar machine to do it for you is pointless and waste of money.
real servers are very expensive, your looking at up into $14,000 from dell for a good server to be able to handle applications. but like i said you dont need that to share files.