There are at least three agencies offering 3-days transfer via the mountains and lagoons to the Bolivian town of Uyuni.
Pamela Tours offered me 3000 pesos discount from the standard 60000 pesos price. We started at 8.30 am by the minibus. It took us in one hour from the level of 2450 m to 4500 m above sea level. On the outskirts of San Pedro there is immigrations post where i stayed plolitely about an hour in the line to get exit stamp in my passport.
Only the last part of the route to the border – some 2 kms was unpaved. In the high mountains there is only tiny and dirty Bolivian checkpoint. They do not have even the toilet. We got entry stamps, eat a field breakfast and boarded waiting Bolivian landcruisers. At the National Park entrance – faw kms further we peid entry fee- 30 bilivianos or 3000 pesos. Bumpy, gravel roads but what a views! Laguna blanca with dozens of flamingoes. First jeep broke here… Repaired after some 2 hours… Laguna Verde – beautiful lake with a volcano in the backgroun. Thermal area Sol de Maniana on the level about 5000 m – fumarolas and mud geysers… Cold night in the primitive hostel – I apprecciated my sleeping bag!