You can develop via on pad as well the prototyping cost for 10 units will be higher but when you are going for 500 units and more than that is for sure that your price will be near above 2$ excluding shipping. 

As per your specification the 10 Unit 15 days delivery will cost you 12$ / Unit + Shipping.

Minimum Drill hole should be 6 mill = 0.2 mm 

500 Units Production = 1$ + Shipping. 

Yes it is feasable to make your project under 10$.

PCB design cost for 0.4mm pitch bga, 0.1mm drill hole, 4-layer routing using via-in-pad
I've noticed a new mechanic in the 5th edition rules that stands out from the rest. It's called Inspiration.

What is this, what is it good for and how should I as a DM grant it?

It looks like it's simply a way to grant advantage for good role-playing? Is this what it's meant for or does it have more meaning than this?
