"It's not very hard to figure out... 2.9% + $0.30"
But ..... you have to figure in the total amount. For example, you're selling something for $100. You tell buyer they have to pay paypal fees. You do some quick multiplication/addition and come up with $3.20 as the paypal fee, and tell the buyer to send you $103.20. Paypal, however, now bases its fee on the 103.20, so your fees are now $3.29, and you end up with $99.91.
The great thing about the site you listed a link to is that you can do a reverse calc, you put in how much you want to end up with, and it calculates the proper amount for the person to send you.
Thanks for the link!