Hi Katy,

you are right, a normal ticket costs 79 Euro one way.

Have you ever thought about travellin over night?
There is a train called EuroNight (EN).
Time of departure is 23:45 and you´ll arrive in Vienna 05:55 next day.
If you book in time you can get it for 29 Euro one way.
That´s rather cheap.

Two possibilities to book.

First:
http://www.bahn.de/p/view/international/englisch/international_guests.shtml

try your travel date and book online.

http://www.nachtzugreise.de/site/nachtzugreise/en/night__trains/euronight/euronight.html

this is about night-trains and EuroNight.

If you have any problems contact the Deutsche Bahn or do not hesitate to ask me.

Hope you enjoy your stay.