I am planning to visit fjords for 6-7 days by the route Bergen - Alesund - Bergen.
Where is better to start the trip from Bergen or Alesund? What are the cheap hotels/cabins by this way and cheap car renting? What are the most attractive places I have to visit?

I will just mention that we went from Bergen to Alesund by bus and enjoyed it. There are lots of ferries and looked to me like it would be complicated on your own to hit ferries at the right time, etc. There were quite a few stops with the bus and then you got off when you were on the ferries. It was "local" -dropping off packages in the middle of nowhere, etc. and we liked feeling we were part of a "Norwegian" experience. No tourists but us. Alesund is wonderful. We flew back from there to Oslo on Braathens.

Going on ferries is not difficult at all. On the main route ferries run all day and theres usually never more than half an hour wait even if unlucky. And while waiting you could have a look around. But having said this, there is nothing called cheap car renting when it comes to one-way rentals. Do a loop getting back to Bergen or take the bus instead like Peggy suggested. Look at it as a tour without the tour guide...

What route to choose is difficult, but whatever route you can't go wrong. As a golden rule I try not to drive more than 200-300 km a day. It's better taking your time unless prepared for a long day on the main road having minimal stops. But even the main road is scenic so it depends on what kind of person you are.

What about flying to Ålesund renting a car there for a couple of days doing the loop Ålesund-Trollstigen-Geiranger-Stryn-Ålesund. There are numerous possibilities choosing is the difficult one.

Thank you very much