Halo should have the advantage of being about $30, leaving you another 30 bucks to put towards another game... The only place I've ever found with Mac games slightly less than full (overpriced) retail is GoGamer.com - pretty reliable, although avoid the cheapest shipping (was $1.99) as it takes forever, and go with the next-highest-but-still-cheap option (was $2.99). I suggest that site b/c you might be able to get another decent title for $30.
However, Halo Intel owners please advise - think you have to digitally download a UB/Intel version for another $5. This is after you buy the game. Not sure if the full version from Macgamestore.com (which also is the only source for the $5 UB download/upgrade) includes the UB, or if you have to buy that extra. Thus, if you can find Halo for $30 like at GoGamer, it may make sense.
...After all of that, I check Amazon and see that they have comparable prices. Halo (but not UB?) for $30, Sims 2 for $34.95. Their shipping IS pretty free & fast.
So, w./some smart shopping, you can get 2 of the games on your list!