Other than the Buhl Centre and the Second-Hand Laden d Caritas at Sankt-Paul-Gasse 12, 3500 Krems an der Donau, there is a handy online site you can use to get second-hand stuff in Vienna, Krems and probably also other parts of Austria. It's called Willhaben.
Idealo is very useful for finding good deals too, but it does not carry second-hand goods.
Both are in German so, Google Translate? Or learn German. Then you will be able to find cheap bicycles to see the beautiful landscape. And maybe cycle to Vienna from Krems in 4-6 hours.
I haven't found a freecycle group yet. If you know one, please mail me about it. I would dearly love to know one exists.