Take the Mears shuttle rather than renting a car. You'd have to pay for parking anyway so the shuttle will probably be the same or cheaper.
For those driving, it's about 30 mins. on a good day from my house, which is right near Disney Hollywood Studios. If I-4 is backed up, you can take 535 to Sand Lake Road and take that across to Turkey Lake Road (right onto Sand Lake, left onto Turkey Lake). You pick up 535 right outside the Downtown Disney gate.