I am doing a round the world trip through Asia, Australia, Fiji and South America and have no idea what to in south America! I have six weeks to get from Buenos Aires to Lima and I dont know whether to book a tour, travel myself, fly, bus, train, commit to booking anything,
Any advice would be much appreciated!
You will be in SA in winter, so some destinations are better than others. It is a good time of year for the highlands of Bolivia and Perú. I would head north in Argentina, visit the Salta area. You can either cross to San Pedro de Atacama in Chile from there (3X a week) or head into Bolivia at La Quiaca. You can get to Arica in northern Chile from La Paz by bus, cross the border there to Tacna and then head north to Lima. Or you can head to Arica from San Pedro de Atacama.
You don't need tours except specific ones in places you find yourself in. Travel overland is easy to book. Forget trains. There aren't enough to get anywhere really. Buses are the way to go. Book lodging in places like San Pedro de Atacama or Cusco, if you are going there before Lima. They are major destinations. Otherwise you can usually find places to stay easily enough. Buses get booked up on long weekends, so be aware of those.
Be sure to check if your nationality requires you to get a visa for Bolivia and what you need to get it.
What would I be expecting to spend in the six weeks including macchu pichu and salt flats?
A tour of the salt flats can run 120-140 US dollars if you take a three or four day tour. Machu Picchu is harder to give a global figure because you need transport to Cusco, lodging there, train to Aguas Calientes, entrance fee etc. That is just going, not doing the Inca Trail (has to be with a company and guide). A wild guess would be 500 US dollars to cover everything but so much depends on lodging and food and how many days you want to stay around Cusco. You should really set aside a week for that. There are bound to be blogs on the internet which you can read.
Bolivia is the cheapest country and you can probably get by comfortably on US$50 a day including food and lodging. Perú is more expensive, but not a huge amount. Chile, Argentina and Brazil are the most expensive and you need around US$100 a day, more in places like San Pedro de Atacama or Patagonia.
If you head to Bolivia from northern Argentina ( a bit cheaper than BA) and cross to Perú from there, you can stick to cheaper areas.