I have done this many times.It has always been just over $20.00. We love to take the monarail from Epcot over to the MK. Then head over to the TOTWL to watch wishes. Then simply head over to the valet desk at the Contemporary and catch a cab.
I took a late night ride between the Poly and the Wilderness Lodge (after the boat stopped), and it cost $8 with tip. I had no idea they were that close together. But, even though they're close, the walk between them, at night especially, would be dangerous (no sidewalks, lots of uneven surface just off the road surface). The alternative was to take a bus to DD and then a bus back, which was crazy, since it could have taken an hour to do it.