One of the conditions of the GPL license that the source code must be made available publically (e.g. something like an ftp website or cdrom) - if you release the program publically.
You can charge as much as you like for the "binary" (e.g. the executable).
You can charge a nominal fee to distribute the source code if it is on a fixed media (e.g. tape or disk).
If you incorporate your own source code into GPL source code then your source code falls under the GPL license too.

The Lesser-GPL (LGPL) allow you to link things like your external libaries into a GPL-licensed program without your external library falling under the GPL.

QT is under a duel-license - GPL and QT-license.
If you write a gpl-license program under QT you do not have to pay any license fees.
If you write a closed-source program under QT a fee is payable.

That's how I understand things - best got advice from www.gnu.org licenses , faq
(I may visit it myself and make sure)