First of all, this isn't coming out with MOJO magazine, but rather with Q Magazine. I know they are two sister magazines, but in this case it is Q Magazine that is putting the CD together, and it will be released with Q Magazine in November as far as I know.
If you want to know what it will cost? Check your local bookstores, and magazine stands and see if they cover Q. It is also important to ask whether or not they will get the CD associated with the issue. In some cases the magazines will not ship to North America with the CD included so you may need to order from overseas.
The other option is to buy via:
http://www.greatmagazines.co.uk/Price for the most recent issue is 5.99GBP, or approximately $9.30US
I'll post the link to the issue with the U2 tribute CD once the issue has been released.
As for the quality of the bands involved in the release, already confirmed is Depeche Mode doing "So Cruel", Patti Smith doing "Until the End of the World", Damien Rice doing "One", and Jack White covering "Love is Blindness". I also heard that Elbow had been approached about doing a cover, but never had confirmation as to whether or not they actually accepted.