It's not much of a secret now, but Aston Martin has, for some time, run a secret car-building operation inside its Prototype Operations. The team will build one-off vehicles for very special, private customers. But the price of entry isn't cheap.

Aston Martin CEO Andy Palmer recently told Road and Track about the secret club, of sorts, and he said his company sells two slots to build bespoke cars every year. Don't get your checkbook ready just yet—all slots are sold out until 2020 at the earliest.

"For those very special customers who want a very special car, we sell two of those slots every year. The next four slots are already sold, and to walk through that particular door, the starting price is two million pounds ($2.6 Million). But they are very special cars," he said. 

For some comparison, these cars are more special than Aston Martin's own Valkyrie hypercar project, which will see 175 units built. Think the Aston Martin CC100 Speedster that the brand built to celebrate its 100th birthday in 2013. Or the GT12 Volante. It's those kinds of cars Aston Martin's Prototype Operations oversees. We can't begin to imagine the tedious planning that goes into an Aston Martin Prototype Operations vehicle. Heck, the process behind specifying a Valkyrie is already pretty darn personalized.

As if we already felt left out, Palmer delivered one last line of secrecy to shroud the operations in: "Some of those cars, by the way, you’ll never see."