Okay, I just signed up for the free 7 day trial as well and when I proceeded to check out, they were asking for me to pay either $10-$15, but then I read at the top on the checkout preview and it stated they charge you $15 for any domain name NOT ending in .ws.
So, then I reviewed the other domain name suggestions which ended in ".ws", found one I liked and then proceeded to check out without having to pay for anything. I even upgraded my free trial to GDI Premium, but I just have to cancel the trial before the 7 days is over to avoid being charged $50. I also requested to add "domain privacy" for $1.00, in order to hide my personal information. And still when I checked out, I didn't have to pay even $1.00. I hope this was helpful!