4 rockets to destroy a Armored Door. That's 5,600 sulfur in raw materials.
2 C4 charges to break a Armored Door — roughly 4,400 sulfur plus metal fragments and tech trash.
12 satchels to destroy a Armored Door in Rust. Satchels have the best damage-per-sulfur ratio on soft sides.
The cheapest explosive option for a Armored Door is 56× Beancan Grenade at roughly 3,360 sulfur.