It's really easy, actually. These days you basically just plug stuff and snap stuff together and you're done, if you've got the right components. I did it for the first time last year myself, it was fun.
If you don't want to do that you can get a good deal over at places like ibuypower.com, basically the same as building it yourself but they add like $200 for making it for you. (Very customizable component wise, which is why I say it's almost like building it yourself.)