Answer:
I believe the answer is "when" because that makes the most sense in the sentence.
Explanation:
" When going to college--even a public college-- is becoming more and more expensive."
So what is the question then?
This is most evidently a metaphor. The thing to keep in mind when analyzing literature/poetry is that if you see figurative language making comparisons/drawing parallels between two differing things--instances where the meaning is not literal such as how injustice is not really a fire and has no flames--it's a safe bet you'll have on your hands a metaphor.