I thought you could set up an automatic Takeout export periodically, and choose the target to be your Google Drive. Then via a webapp oauth you could pull the data that way. Frequency was limited (looks like it says the auto export is “every 2 months for 1 year”). So hardly realtime, but seems useful and (relatively) easy? Does a method like that not work for your intentions?
Downloading from Google drive doesn't cost anything, does it? Although, I guess you would have to have enough empty space on your Google drive to be able to store the takeout zip, which I think is an acceptable cost