In summary, I traded a $100 piece of hardware for a $12 bit of software that allows streaming of iPad screens to my smartboard in a format large enough to read from the back of the classroom.
We've been using Airserver for a couple of weeks now and find it very reliable. The thing I like is that you can have multiple devices on the screen at the same time (e.g. an iPhone AND iPad). Plus there is a PC version as well.