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Damn, sorry, I seem to have messed up with the prices – there's a 2k difference between Novokuznetsk and Novosibirsk (9 --> 7). I guess I was looking for tickets for two people and somehow didn't notice. So, the question of which city to fly to remains open – maybe it doesn't make sense to bother with Novosibirsk for 2k and spend an extra 3-4 hours traveling by bus.
PS. Dirty, if it's not too much trouble, could you estimate the prices and travel time for transfers from Novosibirsk airport and from Novokuznetsk – then we can compare. I think it makes sense to calculate for approximately 10 people.