About the Alu/Steel controversy, there are so many threads on this on BikeForums already, i don't think i want to debate it here once again. But i do think (taste/my view mind you) that steel is a safer bet (especially as the OP experienced back pain on a Alu bike, this may have been related or may not). But i will add that Cannondale do have a reputation for making the finest/most comfortable production Alu bikes around, so YMMV.
I agree that the bikes you were looking into seemed excessively expensive from my point of view and that the extra expense would add little in the way needed performance. I would also recommend looking further into a cheaper more of a do-everything bike. I still stick by my first post as the best possible deal for your cash (custom/woman's fit Bike Friday) but by all means if you don't want to order the aforementioned Trek is a fine bike and all the money you save can go to accessoiries (New Saddle, good cycling clothes, sunglasses, water system) and gear which often are just as crucial as the bike for any long tour. Curious to find out what you decide on in the end!