Can anyone explain this?

I just received a notice from USCIS, they said it time for me to change my resident status from Conditions PR to PR. I went to their site & found out that I need to fork out 600 bucks to do that… can any1 explain to me why? why so much? why do I have to pay those corrupted SOBs $600 just to remove the word ‘Conditions’ from my file? Almost 4 yrs ago, 3k was paid & what I got was like a probation period to stay in USA, it may not seems like a lot compared to others but it’s the 3k that I do not have, for what? So that I do not have to be separated from my soul mate anymore, now in order to continue staying with my family, I have to pay again? I may sound ignorant for blogging this but I just don’t understand why so much, all the troublesome part are already done & over with, now is just a change in status, I can understand a $50 or $100 fee but $600? i jus dont see the justification in it. I mean its like employment, when u’re employed, the initial paperwork are the most troublesome, then u get a probation period to make sure that the employer like u & if they do, ur status change & ure no longer on probation. Now not only my plan of giving Arieanna a birthday bash might go in smokes, I have to worry about being deported, separated from my family that I fought so hard to keep. This is so infuriating! ARGH!