500 quid is only the begining...then there is the ECU and sensors, set of low compression pistons or cylinder-head, exhaust and inlet manifold, wastegate, exhaust system, cooling system, intercooler, oil cooler, workshop/rolling road time and insurance.

So add at least £1K and you have a start budget...then you will probably have to add some mods to the suspension and brakes...which might mean larger wheels and tyres so best make it 2K as a start budget

If you are REALLY serious then strip the body to bare metal and seam weld and strengthen it before you start, so your initial budget will be £5-7K this is where WRC car start...before you even get to the mechanical bits...

If you are only tuning to get the same performance as the factory install it hardly seems worth the effort/expense and would be easier to achieve by either an ecu reprofile/chipping or a cam swap and ecu reprogramming session on a rolling road.

Most factory Turbo installs tend to be more to do with emission control than performance enhancement, agreed there is some improvement to performance but it is at a level which the engine will reliably produce for 100,000's of miles; it is not normally the mind shattering blast to the horizon that you are probably aiming for with 500 quid.

To get that costs ££££££'s and needs lots of skill to control and costs as much again in regular maintenance, tyre replacement etc. Make a few enquiries on the cost of servicing a high performance car and it will be in excess of £300-800 every 10-12K miles. I would guess that your current ride could be dealer serviced for about £150.

Performance costs...high performance really costs...