Food is relatively expensive in Germany. For example, a litre of milk costs 0.5 EUR and bread costs 0.4 EUR.
So for food, at least 100 EUR will be needed per month. (Self-Catering)

Public Transport:  Deggendorf is relatively small, so you may never need public transportation. The city has many taxis and buses. Buses cost 1 EUR for a one-way ride. Around 40 EUR may be required per month.

Most students walk or rent a bicycle.

Accommodation:  Normally costs at least 220 EUR per month

Books & stationery:  You may not be required to buy a book but will need to make photocopies. On average per month, you may need around 30 EUR

Miscellaneous:  70 EUR

In total, you will need around 450 EUR per month

NOTE that during your first month you may need more, because the insurances and other costs have to be included:

Additional information: http://www.fh-deggendorf.de/im-ba/costs.html