Looks like it's free to me. You will have to do some things to allow your XBOX 360 to to use mod packages and such, but if it's anything like the PS3 installation, it's pretty straightforward; takes a good amount of time, but not difficult. Just follow the instructions as they're outlined here:
I'll see how it goes after I've got the MOD packages installed on my PS3 tonight, but I'm pretty excited. I don't think all the teams are done yet (as far as uniforms and stadium updates and stuff; you use the updated rosters like you could before), but it looks like the updates are rolling out fast.