Brasso is one product you can buy for under 50 Euros. You can rub most corrosion spots off with that.
Altrnatively, I've used a simpler and much more cost effect method. Sabesto, is an all purpose heavy duty liquid cleaner. With this stuff you can apply a small amount into a large cup of water. Then put all your corroded fixings in there. Leave it for an hour. Then rub off any remaining spots with a scouring pad. Job done and you've used three sprays from a 20 Euro bottle.