JetBlue, like many airlines, are often sell fares for less on its own site than they do through metasearch engines such as Kayak or online booking sites such as Orbitz. Plus, as do many airlines, JetBlue often throws in added incentives to book on their site. The latest? A $20 credit to your PayPal account, but only if you book on their site.
Example: Ft. Lauderdale to Cancun is on sale for $58 RT plus a boat load of taxes (final price $134 RT) in a current JetBlue sale. But you'd pay $20 more if you booked on Orbitz, and you wouldn't get the $20 credit.
Same flights, same dates found on Kayak (and sending you to Orbitz) $154 RT with tax:
Or you could pay $134 RT if booked directly on JetBlue.com, plus get $20 paid into your PayPal account to spend any way you wish.