However much faith you have in him... There are other people there too... And i'm sure that someone who sees a "skirt" will only see a price tag of $20... rather than $400+...
1 spilt coke... Bye bye kilt... That's not including food... Cigarettes... Fights... And a whole load of other possibilities...

You could maybe get together with his parents and chip in for a stillwater kilt (or similar)... He'd get to keep it then too... And about the same price as a rental ($30 for a thrifty $80 for a standard... Ask for a student discount? )