Hi!
I think this is the cheapest "hotel" in Ålesund. Might be difficult to get a room because of high season though...
http://alesundvandrerhjem.no/node/142
Its in the center of Ålesund and since Color Line Stadion is close to the center its only a 15 min walk.
Prices:
Single bed from NOK 255,-
Single room from NOK 570,-
Double room from NOK 790,-
3 bed room from NOK 890,-
4 bed from NOK 1090,-
5 bed from NOK 1290,-
6 bed from NOK 1490,-
Good luck!