Available at no cost (4)
I believe the answer is:
free
I believe this clue is a double definition.
'available' is the first definition.
(similar in meaning)
'no cost' is the second definition.
(I've seen this in other clues)
'at' acts as a link.
(Other definitions for free that I've seen before include "See 8" , "Complimentary" , "Release; gratis" , "On the house" , "Untie" .)