I think it depends on the airline. On my recent trip I noticed that American Airlines was charging to pick ANY seat. You could avoid the charge by letting it auto-assign the seat. Your idea to check in physically and request a certain seat MIGHT work, but you have to consider the timing. Most other passengers will have checked in online earlier and already have a seat assigned... If you wait until you arrive at the airport the seat selection might be limited. I like to check in online as early as possible so I can decide if I want to pay for a specific seat.
Good luck!
Can you clarify exactly what you mean by a "dumb car"? Do you just mean that it doesn't have a screen in the cockpit? Or something else?