What brand of tyres are on it? You will never make a better improvement to a cars brakes/handling than swapping from budget tyres to premium. Other than that on a tight budget I would keep my eyes open for some used lowering springs, you can probably fit the ARB from another model too, I suspect the RS2000 has a thicker ARB, does your car have a rear ARB? If not you can fit one of these from an rs2000 too.

Rob,