I'll assume this goes for any ToC or Mega-ToC. It also depends on your definition of "asked back to compete". Do you want to count alternates for the ToC since they didn't compete?
I searched j-archive for the last four seasons. These folks were alternates for the ToC, but never competed:
Kevin Joyce: 3-day champ from 4/2009: $113,299
Sara Heard: 4-day champ from 4/2011 $87,601
Among those who never got even an alternate spot, these are the top three winningest champions from the last four seasons that I could find:
Nick Condon: 3-day champ from 6/2011: $82,101
Francis Lansangan: 3-day champ from 11/2011: $80,401
Elyse Mancuso: Teen Tournament winner from 5/2012: $79,600
The answer to your question is probably a 3-day champ. I can't imagine a 4-day champ winning that much money without getting at least an alternate spot.