Part of a hiring decision is based on nonverbal elements in an interview – eye contact, body language, handshake, posture, listening skills, clothing, grooming and accessories. Will dressing properly get you the job? Of course not, but it will give you a competitive edge and a positive first impression.
In job-hunting, first impressions are critical. Remember, you are marketing a product -- yourself -- to a potential employer, and the first thing the employer sees when greeting you is your attire; so, you must make every effort to have the proper dress for the type of job you are seeking.
Dressing conservatively is always the safest route, but you should also try and do a little investigating of your prospective employer so that what you wear to the interview makes you look as though you fit in with the organization. If you overdress (which is rare but can happen) or underdress (the more likely scenario), the potential employer may feel that you don't care enough about the job. How do you find out what is the proper dress for a given job/company/industry? You can call the Human Resources office where you are interviewing and simply ask. Or, you could visit the company's office to retrieve an application or other company information and observe the attire current employees are wearing -- though make sure you are not there on a "casual day" and misinterpret the dress code. When in doubt where a conservative suit.
If you cannot afford two suits, investing in one good suit on a student’s budget is sufficient, until you actually land a job and can afford more. One suit paired with three or four different ties or scarves and shirts or blouses can yield a variety of different looks. When shopping, buy the best quality items you can afford.