What about running the google-drive-ftp-adapter application in your local pc and then connect your filezilla client to that application? The google-drive-ftp-adapter application is not an online service, but its an alternative solution to connect to google drive through ftp.
The google-drive-ftp-adapter is an open source application hosted in github and it is a kind of standalone ftp-server java application that connects to your google drive in behalf of you, acting as a bridge (or adapter) between your ftp client and the google drive service. Once you have running the google-drive-ftp adapter, you can connect your preferred FTP client to the google-drive-ftp-adapter ftp server in your localhost (or wherever the app is running, like in a remote machine) to manage your files.
I use it in conjunction with beyond compare to synchronize my local files against the ones I have in the google drive and it serves well for the purpose.
This is the current github link hosting the google-drive-ftp-adapter repository: https://github.com/andresoviedo/google-drive-ftp-adapter