What to wear to a wedding as a guest?

Ok this is my first time going to a wedding. I hate parties and other little festivities like this. I am a hermit type fella, I don't like to get out and socialize. Anyway my girlfriends cousin is getting married. I don't really want to go but I don't want her family to hate me, so I'm going anyway. This is right after my 22nd birthday(July 2) plus the 4th of July is coming. Guess I should of got with a girl with social problems or one that doesn't like to party. I need help getting a suit for the wedding but I don't want to spend alot of money. I went online and found some suits for $100 but that's to much. I mean I have the money I just don't want to spend alot of money for something I will wear once. And I don't want to rent a suit, I hate renting stuff. Can I just get a cheap pair of slacks, a tie, some payless shoes, and a shirt from wal mart all for around $50? and just get a cheap suit jacket of vest?