Exhaust recommendations please

Hi, I've got a Disco 3.9 EFI (cat model). I've had a look at a few websites. I'm very undecided about keeping the car as my old TDI has come up for sale again and I may buy it back. Does anyone know of exhausts at the cheaper end of the market? Failing that other recommendations?

The Car is running like a pig at the moment with very poor acceleration - I'm hoping the guy in estepona (Spain) where I live can sort it. Airflow?

Thanks guys