You should just buy the orange box. It's only $44.95, that's easily worth it even for just TF2, portal and Ep:2.
Considering I'll never play TF2, and probably never play Portal, and if EP:2 is as long as Ep:1, I'll finish it in four hours, you and I have differing views on worth.
You could also see it the way that you're paying the price for Ep2, TF2 and Portal (20+20+10) and on top of that get HL2 and EP1 for free...
I could, but considering I'm already buying a pack with one game I'll never play and one I may never play, I just wouldn't consider it good value anyway.