I know it's not git deploy.... But Instead of setting up a CI box, I just used s3cmd.
http://s3tools.org/s3cmd
Executing this command syncs my build directory with s3.
s3cmd sync -r ~/code/mysite/build s3://www.mysite.com --delete-removed
I'm using it on Linux. Not sure what their OSX and Windows stories are.
If you're really after a git push solution, you could set up a timed job which pulls your git repo to a folder and then executes this against it. I do this elsewhere on a cheap Linux VM. Unless you're going to go full CI though, there's probably not much point.