Since these games can only be shared with one other person, I would think its worth around $40 or more. Although that would rely on someone liking / needing the games.
Like for instance I already own the disc for MKvDC, Kayne&Lynch. So the value add for me would be less.
What you might be best in doing is working out a deal with whoever purchases the slot to add additional content splitting the cost.

Eg you both want MW3 so you buy it for $35 each paying $17.50, something like that.