If you're renting (leier), you're paying for it. Borrowing (å låne) is free.
Can leier be used for any kind of rent? Like, if I am renting an apartment would I use "leier"?
does this mean that they are the ones who own the bicycles and are renting them out to other people, or that they are the ones who are paying to use them?
It matches up with the English usage:
å leie = to rent
å leie ut = to rent out