Lower still !
And here is SMD BT for $6.60 - although it looks as if default setting would need to be re-programmed if you want 115K
So I could print my own interface to plug into a msp 430, and that would be ~ $10 per (uC + BT) !!
$40 for a 4 bot swarm (not including servos, wheels or batteries)
Seems doable…