If he wants a ricey sound, get him a ricer muffler with a 4.5" outlet. YOu can get a 2.0" inlet and have an exhaust shop put it on. They will cut a little bit of the pipe off and put on a new one that will match up with the muffler inlet size. Since the exhaust pipe size at the muffler end is like 1.75" ( I think, atleast that is what it is on the Duratec dual exhaust). While you are at the exhust shop, have them cut off the exhaust resonator and weld on a straight pipe. The resonator is in the middle of the car on the exhaust pipe and looks kinda like a glass pack muffler, but it is not red.
The muffler will get you a FREE flowing exhaust (atleast on the muffler end) and removing the resonator will get him a little bit more noise (and maybe .00009% of a HP, some people may aruge this though) and it takes a little bit of weight off the car too.
Free flowing ricer muffler (on ebay) $20
install for the muffler $25ish
removing resonator and welding
on straight pipe $20ish
That $65 will get him plenty of noise (to start with).
This is a basic way to start making some noise. ONce he's ready to put some more money for noise and power at the same time, he can look into a MAF adapter with K&N cone filter. This will get better flowing air than a stock K&N panel filter, that goes in the airbox. The MAF adapter eliminates the airbox and a cone filter will be sitting in about the exact spot as the air box. You can hear the intake rumble and hear the air getting sucked into the motor and a more constant rate. This will also help with throttle repsonse.
Tell him Good Luck with his car and start saving up for some real add ons
Dylan