1) If you plan to go to the convocation in your kilt, I would not get a thrifty kilt from Stillwater. To the very least, I will get a Standard model from them.

2) If you can't afford to buy a coat that you are going to wear once a year, rent. It also depends on how formal it is. If you are a engaged college student on a budget, you may be able to get by with only a tie and shirt.