I agree that a sub is not completely essential. Before I bought my Axioms and SVS subwoofer, I had Paradigm Monitor 9s without a sub. I didn't really miss the sub at all with music. And since I had never owned a sub, I didn't miss it with movies, either.

Get the best you can get with your money. If it turns out you don't have enough left for a sub, then know you can always buy one later.