Collecting kief...

I just ordered a grinder with a kief collector, and I'm just curious as to how much would have to be grinded in order to get a useful amount of kief.

The weed that I get is usually pretty good mids. I normally buy $15 to $20 at a time, and it gives me enough to get high everyday for about a week. I don't really deal with "weight" since I don't have a scale, but I do understand that bud can be heavier or lighter than it looks.

So generally speaking, if I grind all the weed that I buy, what's a good estimate on how long it would take for me to have enough kief to sprinkle on a bowl? Or how long would it take for me to have enough to press a good amount?

Thanks

Anybody?