Trip to South American-Help needed

I would like to go travel through South America fro three weeks in August(tentatively the last three weeks) .
I have already been to South America, but I spent much of my time at the cities;Santiago and Buenos Aires, having only one trip out of the city on a dissapointing journey to Colonia, Uruguay.

I would like to know it is possible to do a trip in three weeks passing through the following points:
Arriving to Peru initially....Lima/Cusco*Machupichu-La Paz,Bolivia-Iguazu(Brazil) and Rio de Janeiro.

My budget is limited but I can make average price accommodations.

All information and guidance on transportation and the "must visit sites" will be apreciated.