A VirtualBox machine with the name 'homestead' already exists

I solved by using vboxmanage to get the ID of the VM.

$ vboxmanage list vms
"my-vm" {c700b8b6-b766-4638-871b-736b44b7db18}

Copy the ID of the desired VM (the c700…db18 string) into the contents of ~/.vagrant/machines/default/virtualbox/id. Save the file then run vagrant up to get the vm working without having to destroy it.

For me, the machine was not showing up as an active VM in the VirtualBox application. To fix I had to do this:

vagrant global-status

This gave me the ID of the machine that I needed to destroy. With the ID, run:

vagrant destroy {VM ID}

I had to run that in sudo to actually destroy the machine. At that point, I was able to run

vagrant up