1. Yes, eventually you will want to get all 5 volumes of Card College, but you don't need them all at once.
2. In your particular situation, I would strive to master (i.e. be able to perform in an entertaining way for strangers) the majority of the material in RRTCM before studying Erdnase or ECT. The reason I say this is that IMHO it is better to learn to use sleights in the context of an actual effect.
For instance, it does you no good to have the world's fastest pass if every time you do it you "frame" the action for the audience. You must know how to get into and out of a move without tipping the audience that you are doing something sneaky. The best way to do that is to learn to do the sleight in the flow of an actual routine, coordinated with an entertaining presentation and misdirection. Again: disembodied sleights are cool for impressing your magic buddies, but may not fly in the real world.
To me, Erdnase is stronger in the techinical side of things than in the magic routines. ECT has some good routines, but again, it is techinique focused.
3. Have you considered going the ebook route? This may help you afford some books of routines that will complement what you are learning in RRTCM. For example: http://www.harryloraynemagic.com/newmagicbooks.html
will get you Close-Up Card Magic (a book full of amazingly strong routines) for $15.75 US). I believe Card College also exists in ebook for at Lybrary.com
4. In summary, if you haven't mastered the stuff in RRTCM, keep working on that (there's enough there to keep you busy for a long time), then augment with a book of great effects when you get the cash.