Fix yours truly in money (6)
I believe the answer is:
cement
'fix' is the definition.
(cementing is a kind of fixing)
'yours truly in money' is the wordplay.
'yours truly' becomes 'me'.
'in' indicates putting letters inside.
'money' becomes 'cent' (I've seen this before).
'me' inserted within 'cent' is 'CEMENT'.
(Other definitions for cement that I've seen before include "Seal; bonding agent" , "It's hard" , "Building material to bind things" , "Mortar; strengthen" , "It hardens when mixed with water" .)