Manuals aren't rare at all. They are more expensive though, the price difference between a similar conidition auto to manual can be upto 10-15k!
As for the strength of the 34 auto, there are a few issues with solenoids but generally they can quite happily withstand 200rwkw. As for driving it like a manual, you won't. The tiptronic isn't designed to be driven like a manual and shouldn't be. It is faster to take off using auto, sometimes it is better to shift down for a corner but very rarely.
The manual conversion has been done by a few guys on here and they could tell you the cost.