If it helps, Yellow Cab has gone up to something around 3 bucks to start and close to $2.50 a mile after that. From airport? To general area of hotel? The airport is way up here in the northland, you're looking at just around 15 miles from airport to downtown.
If your hotel is in the downtown-ish area, and you are looking to then go from Downtown Kansas City to the book signing, I would
highly recommend leaving early. Like, pre-rush-hour early. Because you'll be going through the Grandview Triangle to get to the Chipman shopping center. And the Triangle is bad in rush hour.
On the plus side, there's plenty of places to kill time at in the shopping center until the signing.
Speaking of which, having not been to one of these before, is there a recommended time to arrive? So that one isn't stuck outside due to lines or some such, that is.