If you can't afford another suit, try a different shirt or tie with the same suit.
Continue to dress to impress. After all, you are not one of them yet. Even if it means wearing the same outfit, look sharp. It's important to feel good about yourself.
Take note of this job interview advice. Since fit is an important factor, you should compare your qualifications with the job description -- from the company's standpoint as well as your own. And don't forget to research salaries and think about your benefits requirements as well.
Sure, this is a competitive job market, and you will have to sell yourself aggressively. But all this preparation will make you more confident and help you present yourself.