The stickers and t-shirts are meant as a way to help the project while still getting something in return - think of it as a donation with a perk.
As for 1.2k / board - that's quite steep, their BOM (Bill of Materials) should be at most 1/2 of that. A very substantial off-the-shelf 4x (motor + ESC + LiPo) combo will run at the very most for $400.