I would compare and contrast. How many people are they interviewing? Are they interviewing a select few (pay the money for your dream job then), or Hundreds of canidates? How "in the hole would the extra $350 cause you to be? Can you change the dates of the vacation to start later and stay later (or earlier) to not lose two days? Could you just simply extend the vacation? Is it a short or long vacation (where two days might not be that big of a deal)? How many other job opportunities like this come around for you? How do you feel your chances are of getting the job? Could you get an early morning interview and leave right after so you only lose one day of vacation?
For the most part, if this is a job you really, really want--I'd take the interview. You don't have any chance if you don't interview.