I take it you're speaking from experience, you've had a go in the simulators for GP2 ?
Must admit I'm a little surprised to read that.
It really doesn't need to cost that much but, they force you to have a computer engineer and 2 data engineers with you during that time. That is where the price gets extremely expensive.
My biggest issue is rFactor. Which almost every simulator in the world uses. I've driven many different "realistic" mods on rFactor, and I've yet to feel one even close to real life. A Sim trying to replicate the feeling and weight coming from the road, tire, and then to the wheel is failing. They are failing because, and no offense to those that have taken offense, most of the people smart enough to program one of these simulators have probably driven a race car before, but not at the level needed to recreate a proper simulation method. So, the way that the weight changes as you turn a wheel is not correct on any simulator I've driven so far, not even iRacing. So, why bother trying to simulate real life weight with that? Where iRacing gets things right, is the feel of driving in a race against people who you may or may not know. This is something that you get in real life. You may know how the person in front reacts, you may not. It leaves you to have to decipher what the best move is, and that is something that is extremely important in racing. It doesn't matter how fast you are, if you don't know how to set up the correct move at the correct time, you won't be successful.
And we go to the second thing that is truly incredible about iRacing, is how well everything is modeled. I've driven on a few of the circuits in iRacing in various different cars; Suzuka, Road America, Motegi, and Laguna Seca, and I can tell you that I've yet to see a simulator come even 1/4 as close to iRacing in the modeling department. And yet, iRacing I would say is above 95% perfect on the track models when compared to real life. That to me is incredibly vital in a simulator. A simulator is for learning, most of us already know how to drive a race car, and even if it a car we've never driven before, almost every car is driven with the same techniques. Learning the tracks is the more important part in my opinion. If I use rFactor, the tracks are so far off, the only thing I learn is which direction the next corner goes. With iRacing, I can voucher with real life Skip Barber at Laguna Seca experience (Drove the real thing before iRacing), that I was able to use the same braking points, reference points, and turn in points as the real thing, and even more amazingly, my lap time was withing 2 tenths of the real times. That to me, is something that you will not find in any other public Sim.
But I don't see why I need to pay so much for it.
The quality is so much higher as a simulator compared to the rest. It's the same reason why F1 is so expensive. They take everything and turn it beyond 10 and go to 11, that is why it cost more than 2 times as much as an LMP1 team. iRacing in my opinion takes everything they can and then it to 11, that is why it costs more.