Aside from the cost of the standalone unit itself, what kind of price ranges are we looking at to get the car 'tuned'? I suspect this definition changes by the person, but lets just say, acceptable daily driving and some amateur drag racing.
In my opinion, I wouldn't pay all that much because anyone can get the base timing off a stock N54 bin. Nowadays a lot of standalone's offer a form of self tuning for fuel so that cuts time and increases efficiency a ton.
I came from a Megasquirt 2 and its a fossil compared to the newer ones, and getting some tables like: acceleration enrichment, mat density, map scaling was pretty tricky to fine tune and I would gladly pay someone to do those for me
All in all, the price i'd pay varies from engine to engine. N54 single turbo? Not all that much compared to my brothers S38, as there are no base maps out there for that motor, and I don't have a dyno to maintain a specific load and rpm to finely tweak the timing.
Also the fact that the S38 doesn't have any knock sensors and I would have to use det cans, making it just another inconvenience...