All I know is that Mears is NOT a favorite on this board, so you won't get many favorable replies. When we checked, Mears uses busses, and they have a 2-3 hour window of operation, because they stop in several places along a certain route. For example, to get to MCO by 8am, they would probably tell you they would pick you up as early as 5-6am. A CM at BWV told me it took her 3 hours to get from MCO to BWV! That is excessive, in my book. They are probably cheaper, but that is why.
As far as price, it depends on where you are leaving from, the mileage. We (2) took a taxi from the Boardwalk to MCO, and it was $45, plus tip. It would be that no matter how many were in the van. As far as safety, the taxi's are licensed, and authorized to be on Disney property, so they are as safe as any public transportation you could take.