Sorry Home Depot gave me the quote, I went to them and explained it, so a semi-custom door.
No spec on the added soundproofing by adding masonite, except more mass is better.
Heck, Ron Grieva (sp) at Gearslutz adds lead in his custom made doors.
Mine was 48" (I call it the "BFD", big fricking door), so 36" will be less $$
I went with the basic solid core door, in hindsight I wish I added the masonite option.
Way early in my framing phase I bought a pocket door, then decided on not installing it, and framed a 6 foot wide open space and used curtains.
This so I could have a HT space via curtains or a party space with rec room
That was how the basement was 2008 - 2014, then I did this early 2015, framed it for "BFD":
I added 2" 703 as acoustic treatment to mine also for first reflection management.