There is a website you can order it on - cruiselineformal.com and the DJ will be delivered to your stateroom. Prices shown on website.
This is no longer the case for royal caribbean .
As far as the boys are concerned, ours[up to the age of 14] used to wear long black trousers, white l/s shirt and a tie with their black school shoes and they were more than adequately presentable with me in cocktail dress and father in black tie evening suit. After 14 it was school suit and after 18 it was black tie like father.
Cruise line formal prices are not cheap you can get a DJ outfit from around £50 to £100 for mena and have it for use anytime. There were deals at Matalan and Slaters.
There are now 2 ways of ordering tuxedo rental for Royal sailings.
Or by calling the US on 001-800-590-6193