Thank you very much for your interest in respond my questions. The reason a thinking in a Tech III is beacuse I'm in low budget. But now I thinking maybe I can buy a monorail camera instead a folding. They are bigger but more cheep too. And being realistic is better for my economy. Now I'm looking at sinars F (+). For clear the subjets around this thread, that maybe can help other people, I have two more questions:

Bill_1856 say it will cost hundreds the bellows, but doing a search on ebay I found prices around 90 dollars like this one

I found several backs like this one It seems like a tech IV back. This backs match the tech III too?

Thanks