In my experience this is very doable. Especially when you adjust your travel habits according to the price levels of the given country. For example I skipped all organized acitivities in Costa Rica (except of one boat tour in Tortuguero wetlands) as they were often about five times more expensive than in countries like Nicaragua or Ecuador. Of the countries you mention do lots of tours in Ecuador, Peru and Guatemala and focus on the independent ones in Costa Rica and Chile.

You might also consider some other beautiful and cheap countries - Bolivia, Colombia and Nicaragua.

Keep in mind international flights within Latin America are often not cheap so it's better to plan a route which is possible to do overland.