Do you have a normal hourly rate, travel stipend, equipment rental rate.. etc. that you would have charged a stranger to photograph something else - I don't know - flower arrangments or a new fashion line of clothing?

Realistically, the band may never sell 100,000 cd's.  BUT - if they are a smashing success - they may sell millions of cds, who knows.   Either way, it does work out to nice exposure for you.

I would determine what you would have charged a stranger.  I'd draw up an agreement limiting their use of the photograph to just the cd, and to just 100,000 copies.  Make sure you demand a photo credit. 

Ultimitely, Universal may want ownership of the photo and they would have to negotiate with you.  There will be a strong image association with the cd - and it will presumably have many other uses:  print ads, posters, media kits, television stills.  If they want to use the cd image on their marketing - make Universal negotiate for the right.

I know how it is, you want to help the "struggling artist".  You can't give it away.  Well, you almost can and feel good about contributing to their success - but if you restrict the usage of the photo you may have more bargaining power upon their success.

edit:  Forgot to mention merchandising royalties.  If they have a sold-out world tour, that's an awful lot of t-shirts you would want a percentage of.  I guess what I was trying to say is don't give it all away.  Let them do the cd cover, but maybe you can make $ in the end if you restrict the usage.