A rentier's high fee paid up front (8)
I believe the answer is:
retainer
'fee paid up front' is the definition.
(as in keeping someone on a retainer)
'a rentier's high' is the wordplay.
'high' is an anagram indicator (can mean drunk or on drugs and hence disordered).
'a'+'rentier'='arentier'
'arentier' anagrammed gives 'RETAINER'.
(Other definitions for retainer that I've seen before include "Eritrean as kind of servant" , "Fee paid to book professional services" , "The keeper" , "Part payment down for an old servant" , "Family servant; barrister's fee" .)