Personally I'd try to push that ADR back about 1/2 hour.
After the show, you still have to fight the crowd leaving. Once out, I assume if you go back by where the busses & parking lot is you'd find a cab, but you'll be on your own to wave one down (unlike @ the hotel lobby where bell services gets it for you). Depending on how many other folks are doing the same, I'm thinking you may be cutting it close.
As for the cab cost - probably less than $30. That is the most we've ever paid for a cab @ WDW & that included a stop @ 2 resorts (POR & Pop).
If you are going to make that ADR you will absolutely need that cab.