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.