no
Well you can pay money for it but you get it free on most websites, the easiest download is on the Minecraft forums.
Minecraft Inventory editors are completely free do download as they are player made. A few outside the game you can try are InvEdit and InvGrid. A mod for the game that allows you to edit your inventory in-game is called TooManyItems, which I recommend if you know how to mod your game.
It does cost money. but you can download it illegally
No. Demos for games do not cost money.
Minecraft forge is a free program.
No, it does not cost anything.
No they don't.
No
Well, you need the game 'minecraft' which does cost money. Pixelmon is just a mod for the game 'Minecraft'.
Custom maps in minecraft can usually be downloaded for free.
$26.95
They cost memory. No money though.