Huge cost of soil? (5)
I believe the answer is:
earth
This clue is a double definition.
'huge cost' is the first definition.
(I've seen this before)
'soil?' is the second definition.
(synonyms)
'of' is the link.
(Other definitions for earth that I've seen before include "underground shelter" , "Land" , "See 12" , "dirt" , "Familiar example of 1 Across" .)