Dude.. don't go to Acapulco. Seriously. Compared to Cancun, Acapulco is like... Ravenloft. Ugly beaches, ugly town.
Plus, not that it would matter much in the tourist areas, but there's been some violent activity down there these past coupla months. Again, it's more of a "bad part of town" sort of thing, but I'd steer clear anyway from Acapulco this year.
It's unfair to compare it to Cancun, though... that place is literally awe-inspiring. You'd probably find it cheaper to go to Acapulco, but believe me.. not worth it. If you want to consider other Mexican beaches that are not Cancun first go to Playa del Carmen (which is like 30 min from Cancun and you should try to visit if you go anyway) which is also Caribbean and just as or more gorgeous than Cancun... if that's still not an option then Ixtapa, Puerto Vallarta... maybe Manzanillo. Not Acapulco, though... I'm not being funny this time, either.