Most expensive ways to hold sword up (8)
I believe the answer is:
steepest
'most expensive' is the definition.
(steep can mean very expensive)
'ways to hold sword up' is the wordplay.
'ways' becomes 'st st' (two abbreviations for 'street').
'to hold' is an insertion indicator.
'sword' becomes 'epee' (sword used in fencing).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'epee' written backwards gives 'eepe'.
'stst' going around 'eepe' is 'STEEPEST'.
(Other definitions for steepest that I've seen before include "most severe" , "Rising most sharply" , "extremely dear" , "With the sharpest incline" , "Most expensive" .)