Three-day tours from Uyuni, through the salt flats and the Bolivian part of the atacama desert, finishing in Chile, are less than $200 each and are actually the cheapest way to get to Chile from Bolivia. The advantage is that you get to see some spectacular scenery along the way.
Luckily our tour wasn't that eventful. We started in Uyuni early in the morning before heading to a nearby town where locals took salt from the flats to make salt bricks (for building houses) and table salt. Although no permits are required to extract the salt (apparently they have more than they know what to do with), it's not a particularly lucrative business; large salt bricks are worth 15 cents each and packaging a metric tonne of table salt in one kilo bags earns locals less than 10 dollars.
We spent the rest of the first day on the massive salt flats themselves, taking lots of silly perspective shots (Sam thought a few too many) and enjoying a stunning sunset. We were able to get a great view of the scale of the flats from the central Inca Wasy island, a rocky hill full of cactus and petrified coral (a reminder that thousands of years ago, before the water evaporated to leave just huge amounts of salt, this area was part of the ocean). Our first night's accommodation was at a modest hostel here the walls, bed frames, chairs etc were all made out of salt bricks.
Tourists use San Pedro as a base to take day tours featuring geysers, lakes and all sorts of other things we'd already seen plenty of in the preceding couple of days on our way across from Uyuni. One unique sight is the Valle de la Luna (Moon Valley), a rocky red desert valley that really looks, as the name suggests, unworldly. Seeing the sun set over the valley was a particular highlight. After a couple of relaxing days in San Pedro de Atacama we took a short bus ride to the larger, but unremarkable, town of Calama to catch a flight to Santiago