Supply and demand. Everyone and their grandmother makes the blocking enchant for leveling enchanting, because it's cheap and will net a few skillups. Out of the 30 different main specs out there only two of them actually have use for them: Protection Warriors and Paladins. Blood Death Knights and Feral Druids cannot equip shields, the only other specs that CAN and will use shields are Holy Paladins, Elemental and Restoration Shamans. And those three are casters, which means the won't need blocking.
So, you and every other Enchanter on your server made tons of that specific enchant, that only two specs can actually use. No wonder the price plummets to the ground, as the supply must be skyrocketing, whereas the demand is very low.
If you want to sell, do not make scrolls that only apply to very, very, VERY specific customers. Even if they are cheap. Especially not if they are cheap. You won't be able to sell them for a reasonable price.
/edit:
Yep, that's why I'm being paid for my work, and not tipped. Especially if they want my Alchemy CD, than they are going to pay a LOT for it.