The sound (tone,volume) is dictated by the bore of the exhaust, the number of bends (mandrel vs press),the main muffler construction and the resonator. The easiest(cheapest) way to get it louder is to delete the resonator and replace it with a straight pipe. The problem with this is that it can make the exhaust illegal from a noise perspective and also can become very boomy in the car at highway speeds. To get something you're happy with will cost money. Maybe you're better off getting the local exhaust shop to come up with some options for you which you can hear on your car and you work out what you can afford and which sound you like the best.

What ever you do - try and keep the original exhaust so you can put it back to stock when you sell the car. Generally mods will tend to detract from price rather than add to it unless you use expensive brand name JDM gear and even then there is a limit. I know as I've owned over 30 cars and have done money cold before.