BIG POINTS! How can I persuade my parents to let me get a ferret?

I have already done a lot of research and I currently own a 3 year old dwarf hamster so obviously they know I'm responsible enough to take care of one and I think their biggest problem is that "they stink". I know why the ferrets at the pet store smell bad and I know ferrets always have a musky odor that won't really bother us but still they say, "Ewww , ferrets are gross!" So I explained that they will be litter trained and that they are fun- like kittens that never grow up! I also have about $150, which I no isn't that much when it comes to ferrets but will still help. Still no. I may get them over time but my goal is to get them as a Christmas present. Any help will help, THANKS A LOT!!!!!!