Well a bit your details would be nice. What time of the year are you going? Where are you planning to stay (city wise) and what expectations do you have in terms of price / luxury (or lac of for that matter)... Last year at the end of May I biked Passau to Vienna. For the most part we had no problem finding lodging in small inns, but in Linz and Grein we had a bit of an issue finding something affordable and nice at the same time. In Linz we ended up going for a hotel. In Grein we found a nice "B&B"... So time of year is very important.