I wouldn’t say it was build for donkeycar but I put a package in my bootable Lubuntu Donkey ISO which allowed you to turn your rPi into an AP. Tons of stuff on the web for doing that. Range isn’t an issue since it’s already not an issue with the rPi on the car being a WiFi client.
And since you really only need the rPi/Donkeycar on a network to transfer files, I’ve even run the car without wifi and had it automatically going into daemon mode so donkey start up loading a model. In that configuration, you are already in User Mode and can start driving and training. The only thing I didn’t implement was either turning on WiFi to xfer data or a way to signal the rPi to power down so I could safely get the data off the uSD card.
Wifi is really being strung along since it was originally required when the only control was the web browser. With both Bluetooth and RC options, Wifi can easily be turned off most of the time.
here’s my auto hotspot package and scripts: https://drive.google.com/open?id=18qT9IICn4uEVXvY6P4FHGni64GIVeW2K