As a trial to see if it suits you first get a wig.
Or an even cheaper option, if you just wanted that colour for say a weekend event you can get spray on hair dye in silver that goes over the top of whatever colour hair you have. Get enough cans of it and just really go to town, it'll all come out in 2-3shampoos max and no lasting damage at all, although I'd condition it a lot after just to be sure
Most awful photo ever, but I am 99% sure this person has just used lots of spray to get this colour.
Disney Halloween Costume Idea: Ursula | Disney | Disney Family.com