TailGator makes a good point ... buy the 9mm first and then later say you need to buy a .22 because it will save you money shooting the cheaper ammo.
This worked for rifles for me. I bought a .22 magnum first. After a $40 range trip with kids it was easy to that a .22lr would not only be free but would even make me money. Only problem was I still like shooting the Magnum better (and so does everyone else) so i still go through lots of ammo in it.