Overpriced compared to the machines available for the local market, yes.

However, unless one buys a huge transformer, what alternatives are there?

Personally, I am completely happy with the "low end" Zojirushi NS-LLH05 we purchased in Tokyo. The tax refund and the Yodobashi points made the 15k price even better, and it was close to being half the price of a comparable machine bought in or sent to the UK.
If I wanted to do more with it, I'd look for a machine in the 15,000 to 20,000 range which I could buy a replacement pot for (expecting to pay around 6,000yen). Perhaps even buy two pots.
If I wanted a high end model - or a clay pot - I'd buy a transformer and get the Japanese model. Something I intend to do eventually. Don't see how one can get a value equivalent otherwise.