Ford focus

2001 ford focus 65000 miles- my focus is running very rough . when im accelerating and idiling.i have had all spark plugs and wires changed ,air filter, oil and filter. it also has a new battery just put in less than 6 months ago. i checked spark plug gaps. they are right.could my belts need changing? im at a dead end. the car rattles at all speeds and when idiling. sounds like its gasping for air . vroom, vroom up and down is the best way to describe it. can anyone help me figure out what may be wrong? also a guess how much it may cost to repair.