Agree with PP. Having stayed at Disney Vero Beach before, I can confirm that it is pretty isolated even from other places within the city of Vero Beach. Renting a car could possibly end up saving some money over an extended stay just in being able to find some less expensive places to eat offsite (dining can be quite expensive at the resort). And to get to WDW it would cost only a fraction of what it would cost to hire any kind of shuttle service. We were lucky that we drove down in our own vehicle to VB, and then drove over to WDW a couple days.
If you're worrying about driving from VB to WDW, don't. It's an easy drive, just so long as you take the recommended toll roads, etc. If you get off the toll roads too early before getting to WDW, you can run into a nightmare of traffic lights. From VB, just stay on Hwy. 60, then the Florida Turnpike, then the Florida Greeneway and finally Osceola Parkway. This might not be the best "as a crow flies" route between the two, but I think it's worth it. I did a "straighter" route once and it took an extra 45 minutes.