Lascar and Pili can easily be done without guide.
As far as I know there is no public transportation in that direction from San Pedro. The best solution would be renting a car, especially if you are 3 or 4 personns.
You should not need a 4x4, but be carefull, as it is quite a soft sandy terrain. It's a 110 km drive from SPA.
You will have to drive in direction of laguna Lejia. Once ther, turn left before the laguna and follow the tracks as far as you can .... see this picture.
http://www.summitpost.org/view_object.p ... _id=154478
http://www.summitpost.org/image/244674/ ... ascar.html
http://www.summitpost.org/image/244675/ ... lejia.html
After Lascar and Pili, I would strongly recommend you spend a couple of nights at the refuge "laguna Miscanti" and from ther climb Miniques ... extra cheap, super clean and one the most extraordinary spot around.
GPS ponts available here : http://fabriceontheroad.blogspot.com/
look for day 223.