The easiest place to get a cab is the BW valet parking area. We had to split our group in 2001 due to one person getting sick, so I took him back via cab to OKW and left the car with the remainder of the party. The fare was about $6 and I gave the driver a tip to round to $8 given the small distance. The mind is fuzzy, but I remember a flat fee to start and then mileage which isn't much.
On a side note, because Disney's on-site medical center was closed, the valet offered a free cab to Sand Lake Hospital if my friend felt they needed medical assistance. As he felt it had mostly passed, we thanked him and took the cab instead. One other little DIsney magic item - the valet called the OKW guard house to let them know we were coming which greatly expedited our entrance as he just asked our name and room number and wished my friend a speedy recovery.