I'm happy to hear that you enjoyed the demo! Unfortunately, the full game will not be free (we have to make a living!), but it will be reasonably priced and won't break the bank. :)
I'd reckon I'd be happy to pay for it (as long as it is a reasonably long game).
We are planning for an estimated length of 10 hours. That is, of course, subject to change based on average playtimes during beta testing of the full game. But it will certainly be around that length.