I would not get a ferret or any other pet if you do not want one or are not ready for one. They are quite time consuming & quite expensive. They are great pets but they are more difficult to keep than a rabbit or rat (they are great pets too). I would say a ferret is more like a dog, they need shots & regular vet visits & good food (which is more pricey than my large dogs foods), need a good cage which is not cheap, they are very curious therefore get into tons of stuff they aren't supposed to & are known for health problems later in life which consisit of costly blood tests/surgeries. They need a lot of excersize too. thats just the tip of the iceburg. I'm not trying to talk anyone out of getting one but research before getting any pet is a must. A good book is "ferrets for dummies"
I also would not get one just to keep the rabbit company, how about another rabbit?