Opener Bettiss made 78 as North Devon, put in to bat, scored 176-5 in their 20 overs.
With some outstanding, clean hitting, Bettiss stroked nine fours and two sixes.
Fifteen-year-old Jamie Overton played some equally sublime shots, striking three sixes in his 46.
The pair put on 104 for the second wicket before Bettiss was stumped by Matt Allin off the spin of James Ford, who finished with 3-24 from his four overs.
On a slow wicket, Bideford were never able to find the boundary often enough to threaten an upset.
Ford (25) and Allin (29) took them to the halfway stage for the loss of only one wicket, but they had slipped behind the rate and when Jason Hayes (3-25) spun the pair out in successive overs, the game was up.
Overton (2-4) capped a fine evening by taking two wickets in a pacy final over, including clean bowling Mike Wigley for nought as Bideford finished on 126-7.
North Devon now go on to defend their Devon Twenty20 crown against the county's other regional winners.
See Thursday's Journal for a full report, reaction and photos from the North Devon Twenty20 Cup final.