we do not share your data with anyone and there are many ways to control the visibility and storage life of your data here.
but the internet is a public space and you should always assume your data could be compromised.
be smart with your password, use tor or a vpn, and use pgp for sensitive communications.
The fee is not linked to the transaction amount. You could be spening $40 and have a $20 fee or $4000 and fee would still be $20.
primarily dependant on the time of the day you go to make the purchase→