I have signed up for airfare watches to Orlando. 3 times, I have been notified of a fare I’m willing to pay. Each time I’ve logged in on Expedia, gone through the motions, and when I get to the “pay for this flight” page, they up the price by $20-$50. Keep in mind I’m buying 5 tickets. So a $20 price change is an extra $100 on a vacation that is already more expensive than I bargained on.
I’d try Price Line, but the rates are the same unless you name your own price, and NYOP does not allow you any control over flight times.