Hi I did this amazing tour last November. Don't worry about getting currency beforehand, it's better to get pesos when you are there. I can't remember how much cash I took - you don't need too much as a lot of meals are included and you can use credit cards in the hotels. So just bring sterling to exchange. I usually budget the equivalent of around £50 a day when lunch and dinner aren't included and around £30 if you need to buy dinner (including a couple of drinks!) and I usually have just the right amount left over for tips etc.
Bring an international adaptor - you can get them on Amazon or at the airport if you don't have one (and some Boots, Dixons etc. as well). No one in our group had any serious problems with altitude. When in the Atacama you sleep at 8,000ft so not high enough for ongoing problems. During the day you will be at heights of up to 14,000ft - just take your time, drink lots of water. Most people had a bit of a headache, or felt a bit dizzy or breathless for a while but no one was really ill. Bring clothes for every type of weather, from T-shirts and shorts to a windproof jacket and a hat (with a string tie, if possible - it's very windy in Patagonia!).
You will have a wonderful time, enjoy it all! My best holiday ever!
All the best,
Bob
