Sherri, where will you be staying?
If you are traveling WITH 5, that means that there are 6 of you in total? Well, whether there are 5 or 6 of you, that's still more than the comfortable amount for a standard 4-seater golf cart, which means that you're going to have to get the 6-seater, which costs a bit more money.
What you could do as a bargaining chip is to go to a couple places and see what they have available and for what cost. Then go to the next place and say "SO-and-so offered me the week for this price", and so on until you find a reasonable price.
Taxis here sometimes like to rip off tourists. I've been in a taxi filled with my friends traveling about a mile away, and he charged us $15 for three people. Then I've been in taxis with 5 people going from down south all the way to the bridge, and it was the same price.
Generally, you're looking at $5/person/mile; you may end up paying $7/person for 2.5 miles.
Golf cart rentals by the week are definitely cheaper than by the day, and for a 6-seater, you're looking at prices between $550-$650BZ/week.
For me, I'm traveling solo, but I love having the convenience of being able to hop in the cart as I wish, especially when needing to run small errands like buying a pack of cigarettes and a drink. I don't have to sit and wait for a taxi.
Good luck, and let me know before you come if you need the phone number to a few honest taxi guys that I've become close with!