A couple of girls I lived with at uni went after our first year and I regret not going with them. Money was a big concern at the time, but I think I could have made it work by getting a job sooner and being more careful with my spending.
If you're really concerned about the money (seems like you are), maybe save up and go next year instead. It will be hard to get the idea of interrailing out of your head but this year you could go on a sun holiday or a city break instead.