For 50$ (freelancer taxes not included) I will design everything you said in the brief (banner, twitter background, facebook cover, and facebook profile photo) including possible changes, without any extra charge. What can I tell you is that my work is gonna be better than the example you proposed! I will design very professional and I assure you that you will be more than satisfied.
I will try to work perfectly for you, because I am still a beginner (although I made this account years ago, when my designs were not that good) and I need your feedback to raise credibility and get more projects. Pick me!
Thank you!