virtual dj is a great program however unless u have a software controller to use it or time coded vinyl its kinda a pain with just a mouse.
if yer on pc i recommend mixmeister, great program..and u can do alot with it that u cant do with turntables or cdj's
that being said i tend to shy away from programs such as mixmeister because they do all the beatmixing for you, and if yer seriously wanting to get into DJing what are ya gonna do the first time u have to step infront of a "real" set up where u must do everything manually heheh.
so as far as cost to get a good setup. yer lookin around a thousand to get ya started *excluding tunes*
as far as learning how to do it.well i guess if you compare it to lets say guitar its rather easy to learn.
however learning the technical aspects is not even half the battle. the main part about DJing is setting a atmosphere, and how you can take people to other places thru the music, while playing the kind of music they want to hear.
this is called reading the crowd and its the bread and butter of DJing. if you cant make yer crowd dance, yer not a good dj no matter how awsome you are at beat mixing, mashups, key mixing, and on the spot remixes.
edit* almost missed this question what exactly do u need to get started...depending on what ya wanna do. mixmeister is only about 150 smackaroonies.
if thats not the route u wanna go.u must decide wether u want vinyl or cds *or both as most djs use these days* im not sure what you like or what u wanna spin but for most electronic music genre's theres less vinyl releases then there was years ago so u might wanna start with cdjs *only and always pioneer* and get turntables later if u so choose.
other then that u need a mixer *i recommend again pioneer..numark or stanton* and a stereo system of some kind *i use self powered studio monitors so i dont have to hook up a amplifier when im practicing*
and last but not least, headphones. senheiser headphones are awsome for the beginner because they have a great model for about 40 bucks.
but if u have the money go for pioneer brand

hope that helps