Ultrasound for Downsyndrome??

Im trying to figure out if I wanna get this special ultrasound done, to see if there's anything wrong with he baby... I have insurance which covers reg ultrasounds at $20 but my insurance can't tell me how much more this one is, can someone who got this done tell me how much more this one cost then there normal ones?? And if your insurance covered some of it??? 
Thanks!!!!