A lot of Zoins, 7500 in case of the 20 slot pack.
As we got a free storage pane as reward for registering and merging our account with a PlayNC Master Account, I wonder where they would stop with selling "optional" things, as extra storage panes have already been declared optional.
The time requirement for a heavy equipment pack is, depending on how often you repeat quests with multiple chars and so on, around 2-3 months. For very casual gamers it is totally out of reach.
Now let me introduce you to the driving force behind all item mall systems:
Buy an advantage/shortcut/convenience.
Alternatively, pay 4,99$ and get a 20 slot equipment pack from the shop.
Note, I do not suggest this.
But let me play the advocatus diaboli... I mean, we get the 5 slot bag for free, and everything more is optional, right? Who many of use would buy one "just/at least for the main char?" Just the usual item mall trade: Money for convenience, reduced grind.

I am glad that they did NOT do this. Someone at ANet seems to distrust and loathe micro payment systems as much as I do. Thumbs up. But I guess this *might* be a reason why the bags have such an absurdely high cost:
They were meant to be the bait.
The high price, to give players and incentive to shell out some bucks, seems to have been forgotten/ignored after the decision was made not to sell equipment packs.