Apparently it's going to be free: http://www.theverge.com/2015/2/2/7962179/raspberry-pi-windows-10
I looked at the pi2 specs and the price, I was shocked. Around the same price as pi1 and 6x cpu power. This is a fantastic piece of gear to toy around with.
It's very cheap. Around £25 in the UK.
They're sold out everywhere though. I'll give Windows 1o a go when I get my hands on a Pi and it's released, but according to the following article you wont even be able to run office on it: http://www.informationweek.com/software/raspberry-pi-2-six-things-you-can-%28and-cant%29-do/a/d-id/1319064