Most dinner suits off-the-peg need some alterations; usually the trousers are meant for somebody chubbier than the average slim 19 year old. If you can find a suit in a store from which the jacket fits well, then alterations to the sleeve length and trouser girth and length can be done in a few days by a skilled alterations tailor.An even cheaper option is to go to one of the upmarket secondhand boutiques; some vintage dinner suits are beautifully made and often have very little wear on them, and old-fashioned Barathea is pretty durable. If it is a matter of having you neatly turned out for a few parties before you commission your own dinner suit, this would be superior to renting.
Other options would be EBay or savvyrow.com, as long as you don't mind the difficulties of estimating fit sight-unseen.
I think budget internet tailoring with workshops in Asia is fraught with difficulty; in Asia it is hard enough to get proper fit and tailoring, delivered on time when you live locally and can deal with the tailor in person! If the fit or finish is not satisfactory when you receive the goods by mail, you may have a devil of a time returning the goods for adjustment to somebody you have never met. Outside the EU you have very little customer protection at all.
Enjoy your parties!