There are some issues that have not been defined that are delaying the Gertboard. If that statement isn't vague enough sorry but it really does about sum it up. The Gertboard will become available it's just a matter of time possibly measured in month or months.
There is currently one on US eBay for $103 this is double the price
of what it will be when released. There is also a sort of knock off board on eBay as well it's pretty much half a Gertboard not much more than an Arduino Uno type it is going for $50 there are quite a few Pi specific boards available and some that don't take much to convert to the Pi. For the price of the two listed your better off just getting some individual boards. Or waiting for the Gertboard issues to be resolved.
In my opinion if your looking to write code to share your expertise and want to reach a large audience I would go with actually interfacing an Arduino product they are cheap widely available and are multifunction devices in themselves. You would reach a ton of people with your code. If you just want something with the same chip search gert board on eBay (Note the space) and you will see what is there. It is also available on www.web4robot.com
The other if you want to develop your code as teaching tools the Gertboard is the option. Sorry I work graveyard and it's going on 19hours since I slept last. But I hope some of this info is helpful
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