In Austria, the commission fees of the real estate agencies are quite high. These fees will be normally equal to 3 times the monthly rental cost (+ 20% VAT). Note that you should be able to reduce these fees to 1 or 2 time(s) the monthly rental cost (+ 20% VAT) if you reduce the duration of the rent, for example from 5 years to 3-2 years.
Regarding the rental costs, the rents for unfurnished or furnished apartments in Vienna may vary, but it seems that in general the rental costs are lower than in Paris for example.
For more info on the rental types, contracts, districts... Check out the previous posts!