This topic has come up before, so you might be able to search for it and get some more immediate responses.

However, to answer your question. It's usually cheaper to rent a car if you have multiple stops (as it appears you do) and more than say four people. A rental costs around $100 or so depending on what you rent. And a cab ride per person, is around $15 a person each way (without tip).

The other added benefit of driving yourself is that you don't have to wait for pickups, and you can visit the stops at your own pace, knowing you are not on as strict a timeline.