I'm planning a roadtrip to South America for 6 months. How much money should I consider spending there (approximatively)?
That depends where you travel. Bolivia is really cheap and you can easily travel with 60 euros per day. Brazil and Colombia are more expensive.
Try to budget at least 80 to 100 euros per day there. Note that some people are able to spend a lot less by staying at the cheapest hostel and avoid spending money on drinks.
For 6 months, I would say that you need between 9 to 12k.