a real exhaust. just replacing the mufflers but maintaining the stock size piping doesnt really do anything. you need to up the pipe size to either 2.25" or 2.5". the UDP is good but dont spend the money on one from zxtuner. just get one for the focus off ebay for ~$20-$30. with an intake, real exhaust, and pulley you should be around 125WHP. if you can find a header for a cougar it bolts on and that should net you some nice gains as well.
after that your either looking at FI or heads and cams. heads and cams are cheaper but wont net you the gains that FI will.