If we just call the BB push, then we are giving SB odds to call with anything, he is at worst calling. We are losing this (now 6k pot) SO often. We need the SB to cooperate with us or to spike an A or K to win the pot, as you said you aren't willing to commit a lot of chips until you see the flop.
The pot is 6k, we have 7.5k(?) it's going to be tricky to play this hand, I think C/F unless we hit is too passive. We could have gotten heads up with SB's dead money very easily by pushing. He is a large stack, it seems very foolish for him to try and trap out of position so early in a tournament. His calling range is QQ-AA (IMO) the way he has played the hand makes him have QQ-AA a SUPER small percentage of the time. To lose a monster pot all the conditions need to be wrong and lined up for us. To me, this hand is just a perfect storm.
I dont think its an auto call for SB with a mediocre hand despite the odds. He threw out 450 because he had a very big stack compared to the bet, and wasnt sure of BB's interest. Now that he knows both BB and hero are playing for a lot of chips he can fold. If he's willing to play for the 1500, then there is also great risk that he comes over the top here (your QQ-AA scenario) and Im squeezed out of the extra chips.
If he doesnt have QQ-AA, his presence in the hand doesnt hurt us substantially anyway...we drop from about a coin flip to about 30% favorite, but are getting more than enough additional $ in the pot to make up for it. In general I think isolating is a better play with middle pairs than with AK.