Consider renting a "post pounder". Ive put in aprox 400 cedar posts in the past year (8' long and 4 - 8" in diamiter). Rented a pounder for $80 a day and $25 an hour if I want the guy to operate it for me. We pound aprox 90-100 posts a day, 6 minutes per post (average time). Small 3-4 inch rocks are no problem, Big Rocks are a Big problem (fortunatley I have only hit 2 of those).
Very economical way to do it, they are solid as soon as they are done, and its very very quick. If I had to Drill/Auger 400 holes, Id stil be there !
Not sure that works for you or not, but its worth considering