VPS accounts are so low today like $5 or $10/mo -- you don't need a lot of bandwith.
Just set up a development server with that same operating system -- play around without screwing up your production server. wget the wordpress base version then unzip in ssh set it up with the same database name -- wget the theme unzip. Develop> **edit a child theme > Tarball and rsync or wget the files server-to-server then untar.
Or use a gnu/LINUX os (same version os) locally with the identical file paths -- best way
