Yes, it's possible to get an additional development board. Just increase your pledge with $20 and email us (firstname.lastname@example.org) that you want to have one. No additional shipping fees required.
If you would like to get 13 Tags with all the sensors, you can add (according the price list) $19.90 * 3 = $59.70 = ~$60. Add $60 because the total price has to be rounded. So the total would be $199 + shipping + $60. No additional shipping fees required.
But if you do this, you need to also send us an email (email@example.com) and confirm you want 13 devices, not 10.
If any questions, drop us a line :)