No worries at all! I love South America - I went travelling there 'for 3 months'....and stayed for 9!
It is amazing! I went to Peru; Bolivia; Chile; Argentina; Uruguay & Brazil. (it's in my Big Trip link below, and I did kinda what you're planning to do, but the other way round - i.e. I started in Lima)
Bolivia is by far the cheapest country in SA (from my list above anyway), closely followed by Peru. Brazil & Chile were most expensive out of the ones I visited.
The salt flat tour - yeah, you have to do it with a tour, and it's the same jeep and driver the whole way. Your driver is the driver, cook and guide! There'll be about 6 of you in the jeep in total, and it takes you all the way from SpdA to Uyuni (I did it the other way round, so if you're doing it that way you should know you will pay more in Chile as there's less competition since most people do it from Uyuni) I'm so sorry but I can't remember how much it was, but I do know that I didn't rebound in shock at any huge dent in my travelling budget, so it must've been 'OK'! It is really REALLY cold up there though, so be prepared!
Bolivia - I loved Bolivia - it was so random, and traditional too. It's the least developed of all the countries I visited, and it was great to experience that 'step back in time'. It's got so much to offer too - the salt flats; the silver mines in Potosi; La Paz the capital is great too - if you're adventurous, you can do the Death Road bike ride from there! Incredible!
Macchu Picchu is....out of this world!!!! I literally was gobsmacked - when you're up there, and you can feel the effects of the altitude on yourself, it's so amazing to think people could build this kingdom so high in the mountains. I took tha train as I said, stayed overnight in Aguas Calientes, then got up early in the morning to try to get there 'before all the tourists' - it was still really busy though! But, I didn't go with a tour guide, I went on my own, and I'd recommend that (if you're not trekking it) as you can listen in on the tourguides whenever you want by blending into groups, and then you can take off on your own and feel like you're up there on your own, just with the turn of a corner - amazing! I'd also recommend doing the Waynu Picchu climb as I mentioned before - it's pretty steep, but doesn't take much time (maybe 1-2 hours up and down) but the view is amazing. You're going to love it
Feel free to ask any more - I love talking about South America!