In my former job I did a lot of hiring, everything from suit & tie sales people to grunt labor.
I would find out from other teachers what people normally wear.
Being well dressed indicates to most people that you take your work serious, although overdressing can put people off.
I would assume that a suite and tie would be overkill for a teaching gig. If for some reason you need to buy a suit, I would agree with the folks above, do not buy a cheap suit. You may or may not be able to tell the difference, but someone who wears suits on a regular basis can. Here on the west coast we have the Nordstrom Rack, which has the mark-downs and returned items at huge discounts. It is a great place to find anything from a suit or sport coat, to dress pants and some nice shoes. It looks like you are on the other coast so I don't know. I always hated the men's warehouse because they were always trying to sell me something I didn't want.
General unsolicited advise on job interview.
You are there to present yourself so be yourself, anyone who has done interviewing for any length of time can spot insincerity a mile away.