Do I need a big budget?
The price tag really depends on what you want. You travel quite economical if you eat in local restaurants (5.000 - 10.000 COP for a three-course lunch). You can purchase fruit and vegetables cheap on the market. Tourist destinations such as Cartagena or Bogotá are more expensive. You'll quickly spend there 5.000 COP on a beer in a bar while other destinations charge 3.000 COP or even less.
Colombia is not the cheapest country in South America, but certainly neither the most expensive one. Buses and taxis are very cheap, so are national flights if you buy them on time. Shopping is particularly expensive in the bigger shopping malls and supermarkets. And of course, if you buy the imported worldwide famous chocolate spread you miss so much. You'll pay almost 12.000 COP for it.
TIP: Explore the Colombian cuisine and culture what makes it much more interesting and cheap. E.g., Private rooms in Colombian style hotels, are often much cheaper than private rooms in international oriented hostels.
Colombia has a high season, when prices in terms of tourism are more expensive: half December - half January / half June - end July / Semana Santa, in 2018 from March 25 tot April 1st / all official public holidays (+ 2 day before and 1 day after).