Thanks everyone. I ended up going with the blazer, a skirt I forgot I had, and a black wool sweater. It looked really sharp.
And, best yet, I have a second interview on tuesday - they set it up during the first interview, no less.
So I went to Marshalls and found two suits, a blazer, a sweater, and a skirt. All for waht I thought I'd have to spend on one suit. And they, are all really nice brands (one suit is Jones New York, the other is Nine West).