The number of people who worked on the game, the company behind it or how much they learned while making it have very little impact on how much I will pay for a game. If I think I will get enough enjoyment out of it to justify the purchase I'll buy it. If I don't, I won't. I usually take advice from friends and reviews as to what I buy, but since I have access to the mp beta I can judge for myself.
I won't be interested in the single player, I don't spend much time playing single player games, and there are other things I would rather play single player than mount and blade. It's all about the multiplayer for me. Even in multiplayer there are other games I will play more.
As the multiplayer is now, and I think there is still a lot of work to be done, I'd pay $10 for it.
If things go the way I hope in the rest of the beta, and they probably won't as I have very different views to a lot of the people on the forums here, I might go for $20-25 for the multiplayer.
Basicly, $30? Maybe, but I'd be much more likely to go for a multiplayer only version for $20. Or better yet a Steam 4 pack of the multiplayer for $60 then I could get a few of my friends from other games playing.