Yes it is worth it, it is afterall the last day with many of the people at prom youll ever have, it is the culmination of everything and one last day that you might enjoy would be fun. But it is your choice.
If you have a lot of friends, might be. Otherwise, I would spend that money traveling to some place that you think would be cool. If you check, there's a lot of flights to Hawaii or other warm places. Prom may have been fun 20-30 years ago.
I didn't go to my prom and I didn't regret it then and still don't now 20+ years later. My thinking was like yours it's expensive and only for one night, but I'm not a very sentimental person and am much more practical in my thinking. You have to ask yourself, in 10 years might I look back on this decision with regret? If yes then you should go.