Thanks for everyone's feedback - it's been very helpful, and nice to get a sense of what others are doing. I tend to be a planner, but think I sometimes overplan things. But with a family of 4, every penny counts more often than not. I've been pricing my options and this is what I have found thus far:
VIP Executive limo quoted me $240rt for a minivan shuttle for 4, which includes all taxes, port fees, tolls, etc, and includes a grocery stop if we wish.
Happy Limo (Mousesavers recommended) looks to be about $235rt for a town car. Like VIP, price includes all taxes, fees, tolls, etc.