Hi,
Most important, I think, is what surface you will be using them on. Wood aerobic floor = lots of options, but carpeted stage, or OMG! indoor tennis courts or rubber tiles, you need pivot circles and high tops for ankle support.
It used to be my shoes would self destruct after about 3 months but now they seem to be making them better, so looks are deceiving. I put in new inserts/insoles at about 3 months and toss 'em after 6 months at most. I do a lot of rope skipping, cardio kickboxing, and circuit training. With old shoes the whole bottoms of my feet get sore, to say nothing of achille's and calf soreness.
New insoles for about $20US can save you a lot of money if they extend the life of $90US shoes for an extra 3 months.
Rex
Excuse me... May I motivate you?