Kim,
I got 20 (10 pairs), I've not run out yet but I wash everyday! I was going through around 3 pairs a day on average to start with! Luckily for me I don't need to wear them anymore as I have very little leakage. I now only wear them if I go out, Hayden's 10 weeks on monday!
Like pink said you'll need a few to start off with! Better to be safe than sorry!
Hope this helps!
Snoopea