you can find a good silencer for around 3-5000 but i warn you that it'll make you a target in the eyes of the police.
You can fit an RPM to the car as i have seen a few cars with them already in ISB.
I'd suggest you get a good set of rims & tyres and forget the silencer as it'll make the car handle better and make the drive more sporty.
also you could spend some cas on gettng a fresh set of plugs and filter as well as getting the fluids changed in the engine and gearbox etc.