I've been testing V4beta for the last few weeks, and it is much, much better. Many of the common gripes have been taken on board, and there are quite a few new features.
However, the licencing info has not been released. I'd personally hold off until the licencing for V4 is offically announced by Al.
No timescale to releasing V4 has been anounced - they have promised a secuity audit of the code, which will take a while, and I expect there will be documentation to write.
My (uninformed) opinion is that there are many V3 licence holders, and to offer V4 for a free or v.v. cheap price can't really happen (V4 has cost money to develop). I would expect some kind of discount though.
I doubt you'll be able to purchase a licence for at least another month, unless they run out of bugs and already have documentation complete
Jason