So Book 2 only references the Flume Cell as a find or Space Trader item. Book 3 on page 36 says "To leave the system you must use the System Gate. To do this you must have at least one Flume Cell to power the Conduit Drive. These are available from the Shipyard."
I think the general understanding is that every time you use the System Gate (move to the next planet) it expends a Flume Cell. This has been the killer of my games as by the time I reach the second planet I'm unable to purchase a new Flume Cell, fuel and cargo to make the next trip. It's roughly 145c per trip (70/100c for a flume cell or free if you're lucky to find one in a derelict and 45c minimum to straight line it to the planet) so with the 200c starting capital with the 10 grain (which is worth about 100c) You'll need to invest everything you have in the hopes of a 50% profit. Once bad customs roll (which I don't feel like there are many good/neutral outcomes) and you're game is over before it starts. My sample size is small though. I'm 0 for 2 being able to have any cash to leave the 2nd planet I visit. I'm crunching the percentages at the moment to see just how unlucky I am versus how punishing the start actually is.
That said I really enjoy the concept and the charts and the flow. I'll just house rule the tables or starting cash maybe to 2000c instead of 200c to make sure I have enough to get me started.