there have been some issues in the past with island/crystal carts. you might want to run a search to read. i personally will not use them.
*i-do* is right, many outfits are about the same in pricing.
our last 2 trips we used Castle Cars, and got a rate of (around $244 for the week. everything on the cart worked. no problems. they'll deliver and pick up wherever you want. they are always very easy to work with, respond quickly to emails, and always smile.