If you want to go for the basic white frat man "formal", you can't go wrong with khakhis, a button down, tie or bow-tie, and blazer. Loafers / boat shoes or dress shoes.
If you had more than $70 to spend I'd say go get fitted for a two piece suit assuming you have proper body proportions to pull it off. A fitted two piece is the most right thing you can wear to any formal event, and it looks so good nobody is gonna be like "way to overdress" because they're gonna be admiring how sleek your suit is because it's fitted.