Arenas remain expensive, as some might say? (6)
I believe the answer is:
stadia
'arenas' is the definition.
(plural of 'stadium')
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for stadia that I've seen before include "Large sports venues" , "Athletics grounds" , "Bowls" , "large arenas" , "major venues" .)