Ultimately frugal: Everyman has to be (4)
I believe the answer is:
'be' is the definition.
(to be is to live or exist)
'ultimately frugal everyman has' is the wordplay.
'ultimately' indicates one should take the final letters.
'everyman has' becomes 'I've' (where the crossword setter is 'Everyman').
The final letter of 'frugal' is 'l'.
'to' is the link.
(Other definitions for live that I've seen before include "Electrically charged" , "A . . . . wire is a highly energetic person" , "remembered" , "Of TV programme, seen while taking place" , "Reside; given in concert" .)