Most of tax ready in Sofia (3)
I believe the answer is:
lev
'ready in sofia' is the definition.
(currency or 'ready' of Bulgaria)
'most of tax' is the wordplay.
'most of' means to remove the last letter.
'tax' becomes 'levy' (I've seen this before).
'levy' with its last letter removed is 'LEV'.
(Other definitions for lev that I've seen before include "Bulgarian money available" , "Monetary unit of Bulgaria" , "Bulgarian currency" , "ready for trip to Sofia?" , "ready for Bulgaria" .)