ice40UL1K is a $1.60 for a single bga unit on digikey. Probably well under a dollar wholesale. Add in a few cents for a crystal, some capacitors, pin headers, a vreg, and the pcb, probably costs $1-2 to produce.

I should mention that someone capable of doing hobby level bga work could easily make their own at around $30 through a pcb batching service. In terms of electronic complexity, it looks pretty trivial.