Thanks James and Kevin - thanks! I never would have considered PEX but my copper pipes are corroding so my family is ingesting some kind of inorganic copper salt gick which may or may not be better than the organic PEX gick. Changing the water heater anode didn't fix the chemistry - I understand that some anodes can have more or less aluminum or magnesium - I just ordered from Kenmore/Sears by part number and maybe I ended up getting the wrong type. I suppose a special filter right after the well pump could do something. I get the blue water stains only where we run hot water, so one thing I considered was running red PEX for the hot water lines and keeping the cold lines copper (since we only drink from the cold lines). However - my pin hole leak is in a cold water line so there are likely several things going on.
As for cost - I'll have to do some plumbing replacement anyway - I have the one pin hole leak and I see green corrosion spots at many places on the outside of the pipes - particularly around joints. My next ceiling will give me full access, so I for now I can just replace some of the easy runs and most corroded joints and deal with other problems that arise later. The incremental cost is really the difference between copper/PEX joints and runs, the PEX tools and of course time (I'm assuming the PEX goes together faster, which may not be the case).
Anyway - still looking for things to consider. I think a water test is definitely in order and I'll do that before buying the water heater and PEX or copper.
BTW, this is the video that led me to change the anode rod 2 years ago. Interesting to see what is happening inside your copper pipes.