I've booked transfers with Blacklane several times after late flights and appreciated that the price didn't change after confirmation. Last year, I flew to visit relatives for Christmas and arrived late, but the price didn't change. The driver kept track of the flight updates. I read on Blog.Gettransfer How much does Blacklane cost, and they say that, on average, an airport-city transfer costs between $70 and $100. For me, it came out to around $90. They explained what the extra charges are for and when the price is fixed. Are you staying in Seattle for a while? If it's your first time there, I can recommend a couple of cool places.