There's not going to be a market for an O'day 34. Sorry.
What's the price on another Mylar sail? Don't replace the bottom panel, mylar shrinks with age, the entire sail is probably shot, you'll be throwing good money after bad. A tri radial dacron laminate might be a good compromise, but buying used racing sails usually isn't a great idea. Unless, as said above, it's a J24, Melges 24, etc.
Get lots of sail quotes, and you might be surprised at what you can talk your way into.
Merit 25 # 764 "Audrey"