this is awesome, a custum item, wil it be sold on the forum or will it only be one of a kind?

It will be an item the winner can keep. There will only be one. You can't use it ingame or anything, just an item with a customizable name, description and image.

Y is it that expinsive

Because it's your own custom item, a privilege reserved for only the great.

Will we be able to sell it? Or will it be stucked to our inventory?

You can do whatever you want with it. But personally I would keep it for myself.

So would I. But if you got bored of it, and it was the only one in the whole game, then it could be sold for puuuurdy much.

In other words that are simpler to understand, you want only the rich to be able to participate.

So we wouldn't be able to say that we want there to be 3 of the item, and from the winner to have all of them? If I win I would kinda want to have 3 of the item and sell 2 of them ;)

Of course not. Only one item.