First of all not sure if you noticed but at the very bottom of the games description he puts and I quote "Campaign disc ONLY. Game works great and comes with the Manual, 48 hour trial for Xbox Live gold subscription, Halo Reach Beta, and Sgt. Johnson code to use him in firefight. Feel free to ask any questions."
I'd try bidding $20 at most in my opinion if it's just a campaign disc, you'll be done with that in roughly 4-5 hours then all you have is firefight which is meh after a few games I think. I personally thought it was worth it (the whole disc set) because I didn't have any of the DLC for Halo 3 MP so I got all that and an expansion on the campaign at the same time. If anything maybe just rent it if you're only hunting for achievements.