Religious scholar starts to regret actually buying beachfront investment (5)
I believe the answer is:
rabbi
'religious scholar' is the definition.
(I've seen this before)
'starts to regret actually buying beachfront investment' is the wordplay.
'starts to' suggests taking the first letters.
The first letters of 'regret actually buying beachfront investment' is 'RABBI'.
(Other definitions for rabbi that I've seen before include "Spiritual leader of a Jewish congregation" , "Jewish law expounder" , "Legal expert" , "Jewish religious teacher" , "Religious scholar" .)