After considering all that could go wrong with the foundation I think I'll go with poured concrete.

Maybe with a little planning the form material can be used for framing/walls recouping some of the inital expense.

Concrete is currently running around $100/cu yd. If I pour an 8 foot tall wall, 8 inches thick I figure around 37 cu yards. Add in the cost of rebar and I still think I'll be within the budget if I can re-use the form material.

There may just happen to be a NTX MB GTG the day of the pour.

I'm nearly half way done with the excavation. More really big rocks coming out of the hole.