I've been amazed at how long Kia or Hyundai timing belts last. Did a timing belt job on a Kia Sportage last year with 170K miles but the water pump showed signs of wear. So I'm not so sure about luck ... they do last longer than the recommended change interval. Driving beyond the recommended interval is a crap shoot. They could go at any time but usually give you some indication they're about to go. Belt stretch won't allow the car to run right ... there's hesitation when taking off from a dead stop. The water pump may start leaking or making noise.
$700 is a little steep for an Elantra belt change. A good technician should be able to do it in around 3.5 hours including the water pump. Under $500 would be more appropriate. I'd shop around for a better price if I were you.