Any decent ammo is fine for breakin. I do not consider the Euro steel-cased ammo such as Monarch to be decent, so I would stay away from that kind of thing. Where I live, Blazer and Winchester White Box are the cheapest good 9mm. All of my 9mm's feed WWB just fine, but two of them do not like the Blazer.
As for the number of rounds to shoot for breakin -- it varies from pistol to pistol. My Kahr and Bersa needed a few hundred rounds. One Walther needed about 100, and the other needed no breakin at all. My Sigs, HK's, and Glocks ran 100% from the first round. Once a pistol runs 100% for several hundred rounds in a session, I'm fine with it.
I generally run 50-150 rounds per session (depends on how many handguns I bring to the range), and clean between each session.