South America Travel... (best, places, train, time)

[DrEarth]

Hello,
I will be traveling from the US to Sao Paulo...
Sao Paulo to Montevideo...
Montevideo to Buenos Aires...
Buenos Aires to Santiago...
and Santiago to Cusco.

I plan on taking the bus from Montevideo to BA, but I won't have time for long bus trips to the other cities.

My question:
What would be the most affordable way to book everything, as I am mostly sure of my schedule, but if something changes, my schedule will be off, therefore throwing off the prebooked flight dates.

I usually only travel to a few places at once, so this situation is different for me. I'm not the type of person to stick to a strict schedule, and would rather buy a ticket as I go. However, I don't know if this is possible, or if it is, may be way out of my budget.

Thanks for you help!

[Buscape]

Theres a ferry from Colonia, Uruguay to Buenos Aires... I remember it being like 2 hours or so... but cant remember the name... you can buy tickets online in advance... SP to montevideo has buses... but you would have to buy it there... ask someone there about where to buy it and what companies are the best... Buenos Aires to Santiago by bus would be like 24 hours... Cusco can be accessed by plane only through Lima, I believe... There is a train from Bolivia to Cusco I think as well...

[DrEarth]

Hmmm, I would like to take the bus, but I will only have a weekend to travel to the next city, as I need to arrive on Sunday, but could leave Friday night.

A 24 hour ride is possible. However, I wouldn't have the time for a long bus ride from Santiago to Lima. I will look into the bus for all the other cities, and a ferry would be nice too!

I found this site The Bus Station - Americas for bus travel.