Formerly the writing stuff I have was worth a king's ransom (9)
I believe the answer is:
expensive
'worth a king's ransom' is the definition.
I can't judge whether this defines the answer.
'formerly the writing stuff i have' is the wordplay.
'formerly' becomes 'ex'.
'the writing' becomes 'pen'.
'stuff' becomes 's' (this might be a standard abbreviation which I don't know about).
'i have' becomes 'i've'.
'ex'+'pen'+'s'+'ive'='EXPENSIVE'
'was' acts as a link.
Can you help me to learn more?
(Other definitions for expensive that I've seen before include "Charging a lot" , "High in price" , "Very costly or dear" , "not going for a song" , "Pricey" .)