I bought my GS in March 05. The low seat was available as a "no cost" option. The high seat was available for approx £130. I paid up, then moaned at BMW. Why can a short ar$e get a low seat instead of the standard one, but tall people have to pay for a high one. BMW rang to say it was company policy. So that's ok then!
The high seat is definitely worth having if you're on the tall side.