the easiest cheapest way to remove an eastern red cedar stump?

I am helping my neighbor clear about 1/3 acre of stretched eastern red cedar trees. They were planted close together so they would grow tall with very few lower branches, so there are LOTS of trees in this small area. Now that most the trees are cut comes the stump removal. As we all know red cedar is very rot resistant so rotting a red cedar stump is easier said than done. I have researched stump removal online extensively and I get what sounds like good ideas but am sceptical because I am dealing with a rot resistant wood. They are in pretty rocky soil so the heart wood is very abundant. the sap wood rots away pretty quickly in some instances but the heart wood is known to last for over 100 years. I tried drilling holes into the stump and channeling them together to make air vent to burn with diesel fuel but with upwards of 50 stumps it will cost a fortune in drill bits as the chrystaline in the heart wood dull cutters very quickly.

I am not well versed on stump grinders and am sceptical because of the rocky ( lots of rocks the size of basket balls on down) soil. Any and all suggestions will be GREATLY appreciated.