Ethical Dilemma

OOT I need your help.
A friend asked me yesterday if I would write a 7-10 page paper for him. (It is due in 2 weeks) He offered me $125 to do this, and I still wanted to negotiate the price but I agreed in principle. I wrote him a short proposal about my idea which was due today. After thinking it over, I realized that I don't think thats enough money for my time, and I don't even want to write it anyways.
My friend is now upset because he already turned in the idea and he obviously doesn't want to do it. I told him to email the professor or go to his office hours and try to change the idea. I also offered to do some research and help him shape the paper for free.
Am I completely in the wrong here? Also, is anyone on OOT interested in doing this? Could anyone reccommend a place in which he could purchase a paper? Thank you.