The Masonite doors are available in their "Safe and Sound" series which are filled Masonite doors. It's some sort of a particle board filling so it's not as heavy as solid MDF but much heftier than a hollow door. Look around the millwork desk at HD there's probably a pamplet or two describing the Masonite line.

thanks - i looked around and you are right, they do have the safe n sound doors which are somewhat like solid core. the thing i am confused about is, the masonite solid core costs exactly as much as the safe n sound, so which one is better? if the safe n sound is in between solid and hollow, why should i spend just as much on a safe n sound vs a solid core? their website and pamplets aren't very informative...

Solid core doors are just solid thru and thru, safe n sound are solid, fire rated and sound proof. Fire rated from 20 mins up to 60 mins, giving you time to exit if there is a fire. Solid core doors donot block the noise from coming thru.