If you say something is a little bit more expensive, then it is usually between 1%-5% more. If you say something is more expensive, it might be between 10%-20% more expensive. And finally, if you say something is far more expensive, then it can be a any range of values between 30%-100%. Just as an added note, we do not usually judge item prices like this in everyday English. We usually say something is "expensive", "way too expensive", or "a little bit more expensive" when comparing two similar items.

There isn't really a set value for a "bit". On a single dollar, I would say up to about 25%, but if we're talking about millions, a bit would translate to possible far less than 1%. Also, you're number 2 statement "cost a little bit higher" is incorrect. It "costs more" or "the price is higher". :) hope it helps