Google App Engine costs the same as any shared hosting
Every paid app must pay google at least $9 each month regardless of usage.
The main awesome thing about GAE has always been the pay-as-you-need pricing model. This concept is completely shattered now for a certain scale of apps. The Python 3 Wall of Shame needed a few extra DB writes to finish the day nicely which would have cost roughly 10 cents a day. But now google will be rounding that up to 30 cents a day.
Apps that grow to use $1 worth of quotas a month are much better off heading to some form of shared hosting for $5.50 a month until they hit that $9 a month necessity. That's the case with the Python3WOS and another one of my apps. I can't move the wall of shame as I don't have the time to do the porting (locked in ಠ_ಠ), but that other app is simple enough. So google will never find out if it could have been an app that's actually worth $9 monthly.