I think most people here will agree that a GC at the Fort is a luxury that you don't always need, but if you can afford is nice to have. We have stayed at The Fort 3 times and had a GC twice. The first time was for 6 nights and we either took the internal bus to The Meadows and Settlement or, as we were close enough to the Outpost, in the 2800 Loop, we walked. The last 2 times we have had a cart but have also used the internal transportation during our stay as well.
If you want to check it out I compiled a table of distances from each cabin loop to The Outpost, Quiet Pool, The Meadows, and The Settlement that was posted in the following Fort FAQ thread:
*Fort Wilderness Resort Information ( a work in progress)*
There are some off site places that you can rent from and save quite a bit of money if you wanted one for the whole time. IMO it's not worth renting off site if you only want it for a few days. However, as I believe a PP said, you do have to get it on your own, but is easy to do and take about an hour total on each end. When I rented from Kenny's Tee Time this past October I want to say it was about $35 a day including tax. They also let you use their pickup and trailer. It's about a $8-10 Lyfy/Uber including tip each way to the pickup/drop off place so you do have to figure that in if you don't have your own car. But even with that it's quite a bit of savings off the Disney price.