If you have any interest in Science Studies at all, UCSD is, hands down, the best place for you to be. I just returned from my visit there and had the best, most deeply stimulating conversations about the field. The funding at UCSD, while mildly worrisome, shouldn't be a reason not to apply. The way it was explained to me this week was that UCSD is still labeled a "growth campus" within the UC system, which means that funds are distributed favorably there. After the first year, you earn your stipend by teaching, so unless you think there will be some precipitous drop in the demand for comm teachers (highly unlikely when the dept is so popular with undergrads), you're fine.
In terms of your chances, I think it's unwise to think about it by comparing stats. They admitted me and one other person from the comm admit crop to the science studies cohort (there's a separate admit process for science studies), but that's because only two of us indicated a strong interest in the program. The most important metric is the match. Get to know the faculty's work. Be able to talk about it well. Then show that you can situate yourself within the department. UCSD fully expects you to change your mind about what you want to study, so the most important thing is that you demonstrate the flexibility the program would offer you. Also, UCSD trains students in interdisciplinary thinking unlike any other program in the country. Know how to describe why that's important to you. And, of course, get the best scores, letters, and grades you can.
Hope that helps.