Taxis are normally waiting outside all WDW resorts. If one is not available the Cast Member outside will get one for you right away. The fares, of coures, depend on the distance and time it takes to get from point A to B.
That being said, I always recommend to people that the easiest way to get to any Disney resort is to plan on the nearest theme park for that part of the day. From the Magic Kingdom you can monorail over to the Poly, or any of the MK resorts.
Just take the bus from your resort to the MK. Spend some time there and then head over to the Poly.