In reply to JhbGerry:
Solo is very expensive, if you got in peak season the park permit is now $1200 for a westerner and unless you're planning on lugging all your own food & kit the entire way you are going to end up shelling out for meals at the basecamps.
There's a company in Mendoza called Inka, they were our local company when we went in January and couldn't recommend them enough. We had various difficulties from the road to los penitentes being closed due to landslide, to people getting AMS and having to be carried out on mules, Inka came up with solutions really quickly. Their set up at basecamp is one of the best, food's plentiful and really good (just avoid the soup!!) and they're a really nice bunch to top it off.
Through Inka our park fee was only $800 which is a good saving but offset by paying their fees, we did full-board with them and for me it was worth the money for taking away many headaches, those we saw soloing looked utterly burnt out.
Met a brit who had tagged on to an Inka group with 2 Canadians, a few norwegians and a kiwi so there's a good mix of folk trying it.