I haven't encountered anything that has required or prompted me to pay, yet.
It plays well I think. You give orders simultaneously with enemy, then hit play and your orderes play out in realtime for like ten seconds, then its time for turn 2. Thats in SP anyway, I imagine (and hope) its the same in MP. Whats cool is you can avoid shots by altering course etc. Also Friendly fire is on, collisions with any other ships/rigs/rocks hurt. Ships can go out of control, have bridge destroyed and go blind for a round etc. I like it, personally.