That you're thinking about this at age 19 is cool to me, IMO.
Certainly, jeans are the expected and most accessible attire choice. It's all I generally wore at 19 unless I was required for work, a wedding, or some other event. But the truth is there's a lot more out there than jeans -- and jeans all the time can be so one dimensional, as you note.
And if someone is 19 and dumping hundreds of dollars on just one pair of jeans, they could easily get a great pair of "non-jeans" pants for that price. Not necessarily bow-tie-and-tux, but something that is classy, has clean design lines, fits extremely well, and might even fool people into believing you're a person of culture and taste.
To spend $300 on jeans has become, to me, like dumping all of your money to trick out your Honda Civic... when you could instead buy a nice BMW for the same price.
It's better on the East Coast of the US, for example, than it is out West here. People are casual all the time in California, where you see people still dressing up for an evening out in places like New York. About the only place to see people dress up in SF anymore is the opera ... I've even been to the symphony where most of the people showed up as if they just got out of the gym.