Have the same stupid passenger seat issue on my 06 LX. Quoted like $1500 or something ridiculous! We just ignore the light, but I may consider pulling the bulb sometime in the future. We have 90,000 miles on ours and were second owners so it would be our dime... which it won't be. Grrr! Problem started around 83,000 I think.
Good luck with yours! Between the insanely expensive seat cushion issue and the slowest gear hunting of an automatic that I've ever experienced, I'm not a loyal hyundai enthusiast anymore.
2006 Hyundai Sonata LX in white with chrome OEM wheels