Hi - I've just returned from the latest trip - Peru is a wonderful place to visit. I took £500 in Peruvian Sol and spent nearly all of it (approx 4 sol = £1) - but I did buy some beautiful jewellery in the better shops in Pisac plus lots of other gifts. There are markets everywhere with great vfm purchases so keep some space in your case if you want lots of gifts or memories for your home!
Everywhere will take US $ as an alternative if you don't want to gamble on local currency. It's also easy to find an ATM machine in Lima or Cusco - or at the airport between one of the many flights! Obviously using an ATM has a cost attached but you can get Sol or US $. Many shops and the hotels all take credit cards but note some only take Visa or Mastercard so if you plan on using credit cards for purchases then it might be wise to take both if you have the option.
We all tipped the local guides who provided the tour information on the visits - so in Lima, Cusco, Puno and the Amazon - we also tipped Rosario at the end - she is absolutely great and you will feel her management and personality add enormous value to the tour. There are guidelines for tipping but you should also give what you feel you can afford - I used about 400 sol for tips.