Mongo Atlas outbound data costs

Before building on it I’m trying to gauge the cost of leaving MongoDB’s Atlas cloud hosted database service, but I can’t find anything in their official documentation about outbound data costs. I did find a third party claiming 9 cents per gigabyte to transfer to the general Internet but I really don’t want to rely on this.

Does Mongo publish official figures on this somewhere? If not, does anybody know them from direct experience? Or know how I could find them out?

Mostly I’m trying to sense how hard they’re going to try to "hold my data hostage" if I ever become dissatisfied with the service.

Thanks