If you want to save a bit of money on car repairs then you could opt to source and buy the parts yourself. If you have a garage or mechanic that you wish to use you will need to check if they are happy for you to provide them the parts to fit. If you do decide to do this then obviously it will only be their workmanship that is covered by any guarantee, not the parts that you have supplied.
Sometimes you may be able to get the parts a lot cheaper than the garage quotes you but you do need to make sure that you know exactly what part you need and if you are buying second hand that it has a warranty on it and it works as it should.
Some places such as Euro car parts offer non genuine parts at great prices and if you can find a voucher code you may be able to save even more on the purchase price.