you need a decent turbo, a manifold making up, intercooler, some sort of managment for fueling, exhaust down pipe, oil cooler, bigger brakes, better clutch. turbo pipework and hosing. some way of lowering the compression.
then you have the cost of mapping the car to set the fueling.
you are looking at a few grand there just for a basic setup.
its has been done alot cheaper and can be done cheaper if you know what you are doing.
my advice would be to think hard about it and save hard.
its not good cutting corners to save a few quid here and there, you are placing excess stress on your engine and something will give if you do the cheap bodge job option.
you will pay the price big time.
please dont fall for the, get your car turbo'd for £500 crew.
you can have a reliable setup, that will give many cars a really good run for there money and put a really big smile on your face every time you drive it.
for big boost and big power you need to play with the internals and lower the compression and use stronger forged low comp pistons and forged con rods.
it can be done and there are many big power saxos out there that will upset alot of performance and dare i say it supercars