Of course they provide samples. I've got a couple of those Stratix 10 devices for prototyping from the client for free and I'm pretty sure they also got those either free or at low cost from Intel/Altera. Also, they were giving me 3-month keys for their full Prime software several times while developing, also for free.
However, I seriously doubt their part would be SIGNIFICANTLY cheaper if somebody decided to go into production with those. Maybe 10%, even 20% cheaper but even 50% is unrealistic.
I built first prototype WITHOUT the FPGA to test all power supplies (that took half of the entire PCB) and program power sequencing to make sure it is right. Only then boards with FPGAs were built so didn't blow that "el-cheapo" part.